Hello,
Since I noticed that even Per's Ultimate guide (fantastic stuff) kinda misses a point on how powerful the NPCs are in this game, and suggests terribad weapon choices for them, I decided to write some of my own thoughts on the matter.
I mostly play in 5-man parties for a good reason: it's fun to watch them rape stuff. Around level 12, a typical small guns build can barely kill a raider in three turns, whereas your NPC team can easily kill three and more. It takes sniper perk and bonus RoF to even stuff up, but expect them to kick a lot of butt until the very end.
Of course, it doesn't happen if you follow Per's advice and give Cassidy shotguns and stuff... no offense, Per
So, here's my list, from best to worst:
Sulik - The best NPC in game, and the wide range of weapons he's proficient in makes him useful in almost all stages, unlike Vic which plain sucks early on. The trick is to set him to "Charge!" and give him an SMG (ideally a H&K P90c) - this will cause him to run up to a target and unload a clip right in his face, and with 43% critchance (if you use the stage 6 NPC fix, he really reaches that!), you can expect him to automatically kill a LOT of critters. It's pretty fun because at stage 6 he has 13 AP, enough to burst two guys down in quick succession if they're not far from each other. He's pretty useful against enclave guys too with a mega power fist and some drugs, allowing him to smack them 5 times per turn and practically murder whomever he latches to. A great guy and great fun to watch him murder stuff. Oh, and he reaches stage 6 VERY early on (level 20) so you can actually have him at his max potential even if you're not leveling up on wasteland encounters at all.
Rating: 10/10. Amazing from start till finish.
Cassidy - I think there's a lot of unexplained love going for Cassidy, simply because whenever he's used "traditionally", he just plain sucks. He doesn't reach 10 AP long until his final stage (which happens at level 22), so he can only shoot once per turn - and most people tend to give him terrible weapons like shotgun, making him do like 15-20 damage at best in a single turn - highly unimportant.
A better idea is to set him to "Charge" with an Assault Rifle in hand - because of lack of AP he won't spray as many people as Sulik, but he will still deliver devastating blows to most of soft targets (like Raiders, Centaurs, New Reno families). as his abilities grow, he will also score more crithits which ignore armor, making him proficient even against Aliens and stuff, whereas he'd be totally useless with typical shotgun&stayclose to me settings.
Eventually, he reaches 36% crit chance and an ability to use gauss rifle, making him the best sniper NPC in the game. And just for that, it's worth to get him.
Another way to make him NOT suck in the middle of the game is to give him a mega power fist, he's quite accurate and will deal 2-3 times more damage than with shotguns or any single shot weapons.
Rating: 8/10. Not as fun as Sulik, but makes up for it later on.
Vic - A mixed blessing. On stage 6 (if you enabled it), he gets 12 AP - enough to shoot three times with certain weapons - and a LOT of energy weapons skill, which makes him amazing Alien Blaster user. On the other hand, earlier on, he doesn't have the "Charge!" setting and he's stuck doing pitiful 10-20 damage with a small single shot weapon of choice. The sad part is that he also sucks in melee/unarmed so you can't even redeem him with a megapower fist. He's deemed to suck until he reaches 10 AP - by that point it's recommended to give him a Needler pistol (from myron, for instance) with the stronger AP ammo - that will turn him into a formidable damage dealer. Later on it's either gauss weaponry or alien blaster, whichever you prefer. Crit chance - 22% on final stage, kind of a letdown but with alien blaster his damage output is still great anyway.
Rating: 5/10. Very useless early on, practically dead weight, but picks up in late stages. I'd pick him tho.
Marcus - Even a bigger mixed blessing than Vic. Around level 12 and around New Reno he's the BOSS, doing 60-200 damage per round depending on how you set him (I recommend- again - Charge! and a big gun, like a Minigun, and a Bozar later on) - but as the game progresses, he becomes pretty soft and pretty weak. And no, it's NOT because of lack of armor (not to mention Killap's RP has an armor suit for him) - but it's because he is limited to "Charge!" and "On your own" settings. If you want your NPCs to survive in Navarro and/or Enclave, you absolutely MUST set them to "Stay close", or they will wander out of the room/chokepoint you're at and get slaughtered by multiple high damage guns, with no amount of armor saving them. Another thing that sucks ass about him is the terribad speed - he's just slow, and it's annoying to wait up for him every time you want to initiate combat.
So, what to do with him? Picking him up around levels 12 turns the game into EZmode, as - armed with minigun or plasma rifle - he's death sentence to poor suckers like raiders or mordinos. However, around Navarro, he starts to be a liability. Unless you intend to edit the TXT file to give him the "stay close" command, dropping him may be the best idea in the late late game.
Still, it's fun to see him blast tough deathclaws to pieces with one good minigun critical to the face. And don't worry about burst damage - charge! setting is very safe since he'll only burst against targets right in front of him and avoid it if he can hurt you or NPCs while doing so. Crit chance - IIRC 26% on final stage.
Rating: 6/10 - if only he wasn't so slow and suicidal later on.
Skynet - Oh well... 121% science check and a LONG level-up path (final level IIRC at level 26... if you pick him up at level 10, that is) makes him retardedly high to keep leveled up within typical game's boundries. In addition, he cannot use chems, so forget about him saving his metal ass by super stimpacking when wounded, he'll just die - forget about psycho to make him laregely impervious to burst weaponry as well. On the other hand, he starts with 10AP (making him a good candidate for rifles), has all the combat settings (you're welcome to give him an SMG and make him charge), is very accurate, and has an auto-heal option after combat. A VERY mixed blessing and probably not worth the fuss, but if you want five team members... he's your man. Robot, I mean. Pretty useless in Enclave because he cannot heal himself in combat, meaning he will die sooner or later.
Since there's not really much to pick over him. Crit chance - iirc 25% on final stage - good, but not overwhelming.
Rating: 4/10, mostly due to retarded skillchecks and shortcuts you have to go through to pick him up earlier on, unless you want to be stuck with stage 2 or stage 3 skynet in Enclave.
Goris - oh well. If you hoped stage 6 would help Goris... you were wrong. Goris is fun, but has several fundamentally wrong things about him that make him a liability.
1. He comes very late, forget about getting him leveled up fast without stupid shortcuts
2. even if you pick him up with shortcuts, you still need level 30 to see his final stage (ouch)
3. He tends to miss A LOT for some reason, especially on lower stages.
4. His damage output is super random. One time (on stage 6) he hits the target five times doing 20-30 damage (with crits up to 90), other times he does 2-5 points of damage per hit and misses a hit or two.
5. He cannot use chems. This is terrible later on - he gets critted and he dies, he can't even heal himself.
6. His only setting is Charge!. As with Marcus - useless in Navarro or later, he will just wander out of chokepoint and die.
7. As hard as he tries, he just cannot match Sulik's damage output if Sulik has mega power fist.
8. His hide is pretty "thin" (Marcus and Skynet both have better DR/DT iirc).
9. You can't plant items on him! (why...?). It says there's no space left, meaning you have to do it via trade window, which is slow and annoying.
On a positive note, he does tend to kick some butt (compared to shotgun Cassidy at least) if you pick him early on (say, around level 9-10), but it's obviously nothing compared to NPCs set up to Charge! with burst weaponry. You can also use psycho on him, which is recommended against Raiders and Mordinos/Bishops, but there's sadly nothing to protect him from energy weapons. Funny little NPC, but too fragile and too lame in damage potential. Crit chance at stage 6 is 29% - kinda disappointing, isn't it?
Rating: 3/10
The rest: Honestly, those are the only NPCs I use, simply because everything else is inferior and not worth a spot. This sadly includes new RP NPCs which either have low AP (can't shoot twice), or low bad crit chance. I wouldn't bother with'em.
And a hint: Tesla Armor + Psycho is a combination that works WAY better in keeping NPCs alive in Enclave than Hardened Power Armor. Believe me.
oh yeah, and a small myth buster: "unarmored" NPCs like Marcus and Goris are actually tougher (as if: it takes more shots to kill them) on final stages than human NPCs in Hardened Power Armors against weapons like Guass Rifle and Plasma Rifle, with the exception of Sulik. Yes, I did the math. Yes, I'm a nerd. Yes, Per is wrong. Sorry Per
What really kills them is the lack of "stay close" option and/or inability to use super stims.
Since I noticed that even Per's Ultimate guide (fantastic stuff) kinda misses a point on how powerful the NPCs are in this game, and suggests terribad weapon choices for them, I decided to write some of my own thoughts on the matter.
I mostly play in 5-man parties for a good reason: it's fun to watch them rape stuff. Around level 12, a typical small guns build can barely kill a raider in three turns, whereas your NPC team can easily kill three and more. It takes sniper perk and bonus RoF to even stuff up, but expect them to kick a lot of butt until the very end.
Of course, it doesn't happen if you follow Per's advice and give Cassidy shotguns and stuff... no offense, Per

So, here's my list, from best to worst:
Sulik - The best NPC in game, and the wide range of weapons he's proficient in makes him useful in almost all stages, unlike Vic which plain sucks early on. The trick is to set him to "Charge!" and give him an SMG (ideally a H&K P90c) - this will cause him to run up to a target and unload a clip right in his face, and with 43% critchance (if you use the stage 6 NPC fix, he really reaches that!), you can expect him to automatically kill a LOT of critters. It's pretty fun because at stage 6 he has 13 AP, enough to burst two guys down in quick succession if they're not far from each other. He's pretty useful against enclave guys too with a mega power fist and some drugs, allowing him to smack them 5 times per turn and practically murder whomever he latches to. A great guy and great fun to watch him murder stuff. Oh, and he reaches stage 6 VERY early on (level 20) so you can actually have him at his max potential even if you're not leveling up on wasteland encounters at all.
Rating: 10/10. Amazing from start till finish.
Cassidy - I think there's a lot of unexplained love going for Cassidy, simply because whenever he's used "traditionally", he just plain sucks. He doesn't reach 10 AP long until his final stage (which happens at level 22), so he can only shoot once per turn - and most people tend to give him terrible weapons like shotgun, making him do like 15-20 damage at best in a single turn - highly unimportant.
A better idea is to set him to "Charge" with an Assault Rifle in hand - because of lack of AP he won't spray as many people as Sulik, but he will still deliver devastating blows to most of soft targets (like Raiders, Centaurs, New Reno families). as his abilities grow, he will also score more crithits which ignore armor, making him proficient even against Aliens and stuff, whereas he'd be totally useless with typical shotgun&stayclose to me settings.
Eventually, he reaches 36% crit chance and an ability to use gauss rifle, making him the best sniper NPC in the game. And just for that, it's worth to get him.
Another way to make him NOT suck in the middle of the game is to give him a mega power fist, he's quite accurate and will deal 2-3 times more damage than with shotguns or any single shot weapons.
Rating: 8/10. Not as fun as Sulik, but makes up for it later on.
Vic - A mixed blessing. On stage 6 (if you enabled it), he gets 12 AP - enough to shoot three times with certain weapons - and a LOT of energy weapons skill, which makes him amazing Alien Blaster user. On the other hand, earlier on, he doesn't have the "Charge!" setting and he's stuck doing pitiful 10-20 damage with a small single shot weapon of choice. The sad part is that he also sucks in melee/unarmed so you can't even redeem him with a megapower fist. He's deemed to suck until he reaches 10 AP - by that point it's recommended to give him a Needler pistol (from myron, for instance) with the stronger AP ammo - that will turn him into a formidable damage dealer. Later on it's either gauss weaponry or alien blaster, whichever you prefer. Crit chance - 22% on final stage, kind of a letdown but with alien blaster his damage output is still great anyway.
Rating: 5/10. Very useless early on, practically dead weight, but picks up in late stages. I'd pick him tho.
Marcus - Even a bigger mixed blessing than Vic. Around level 12 and around New Reno he's the BOSS, doing 60-200 damage per round depending on how you set him (I recommend- again - Charge! and a big gun, like a Minigun, and a Bozar later on) - but as the game progresses, he becomes pretty soft and pretty weak. And no, it's NOT because of lack of armor (not to mention Killap's RP has an armor suit for him) - but it's because he is limited to "Charge!" and "On your own" settings. If you want your NPCs to survive in Navarro and/or Enclave, you absolutely MUST set them to "Stay close", or they will wander out of the room/chokepoint you're at and get slaughtered by multiple high damage guns, with no amount of armor saving them. Another thing that sucks ass about him is the terribad speed - he's just slow, and it's annoying to wait up for him every time you want to initiate combat.
So, what to do with him? Picking him up around levels 12 turns the game into EZmode, as - armed with minigun or plasma rifle - he's death sentence to poor suckers like raiders or mordinos. However, around Navarro, he starts to be a liability. Unless you intend to edit the TXT file to give him the "stay close" command, dropping him may be the best idea in the late late game.
Still, it's fun to see him blast tough deathclaws to pieces with one good minigun critical to the face. And don't worry about burst damage - charge! setting is very safe since he'll only burst against targets right in front of him and avoid it if he can hurt you or NPCs while doing so. Crit chance - IIRC 26% on final stage.
Rating: 6/10 - if only he wasn't so slow and suicidal later on.
Skynet - Oh well... 121% science check and a LONG level-up path (final level IIRC at level 26... if you pick him up at level 10, that is) makes him retardedly high to keep leveled up within typical game's boundries. In addition, he cannot use chems, so forget about him saving his metal ass by super stimpacking when wounded, he'll just die - forget about psycho to make him laregely impervious to burst weaponry as well. On the other hand, he starts with 10AP (making him a good candidate for rifles), has all the combat settings (you're welcome to give him an SMG and make him charge), is very accurate, and has an auto-heal option after combat. A VERY mixed blessing and probably not worth the fuss, but if you want five team members... he's your man. Robot, I mean. Pretty useless in Enclave because he cannot heal himself in combat, meaning he will die sooner or later.
Since there's not really much to pick over him. Crit chance - iirc 25% on final stage - good, but not overwhelming.
Rating: 4/10, mostly due to retarded skillchecks and shortcuts you have to go through to pick him up earlier on, unless you want to be stuck with stage 2 or stage 3 skynet in Enclave.
Goris - oh well. If you hoped stage 6 would help Goris... you were wrong. Goris is fun, but has several fundamentally wrong things about him that make him a liability.
1. He comes very late, forget about getting him leveled up fast without stupid shortcuts
2. even if you pick him up with shortcuts, you still need level 30 to see his final stage (ouch)
3. He tends to miss A LOT for some reason, especially on lower stages.
4. His damage output is super random. One time (on stage 6) he hits the target five times doing 20-30 damage (with crits up to 90), other times he does 2-5 points of damage per hit and misses a hit or two.
5. He cannot use chems. This is terrible later on - he gets critted and he dies, he can't even heal himself.
6. His only setting is Charge!. As with Marcus - useless in Navarro or later, he will just wander out of chokepoint and die.
7. As hard as he tries, he just cannot match Sulik's damage output if Sulik has mega power fist.
8. His hide is pretty "thin" (Marcus and Skynet both have better DR/DT iirc).
9. You can't plant items on him! (why...?). It says there's no space left, meaning you have to do it via trade window, which is slow and annoying.
On a positive note, he does tend to kick some butt (compared to shotgun Cassidy at least) if you pick him early on (say, around level 9-10), but it's obviously nothing compared to NPCs set up to Charge! with burst weaponry. You can also use psycho on him, which is recommended against Raiders and Mordinos/Bishops, but there's sadly nothing to protect him from energy weapons. Funny little NPC, but too fragile and too lame in damage potential. Crit chance at stage 6 is 29% - kinda disappointing, isn't it?
Rating: 3/10
The rest: Honestly, those are the only NPCs I use, simply because everything else is inferior and not worth a spot. This sadly includes new RP NPCs which either have low AP (can't shoot twice), or low bad crit chance. I wouldn't bother with'em.
And a hint: Tesla Armor + Psycho is a combination that works WAY better in keeping NPCs alive in Enclave than Hardened Power Armor. Believe me.
oh yeah, and a small myth buster: "unarmored" NPCs like Marcus and Goris are actually tougher (as if: it takes more shots to kill them) on final stages than human NPCs in Hardened Power Armors against weapons like Guass Rifle and Plasma Rifle, with the exception of Sulik. Yes, I did the math. Yes, I'm a nerd. Yes, Per is wrong. Sorry Per

What really kills them is the lack of "stay close" option and/or inability to use super stims.