Personally, I think the modded Hellfire armor is pretty sick looking. What it lacks in charisma and radiation resistance, it makes up for in strength and fire resistance.
I will say that excavator armor from 76 reminds me of weird 90s cartoons and toys, so I was fond of it. I don't think it really fits the universe well at all, but there's some janky design about it that I liked. Kinda reminds me of Beetleborgs for some reason.
The first time you get a suit of T-51 power armour in F01 is great. Felt for the first time that I actually was a walking tank.
I guess it's because power armour isn't really needed at all in the 3D games, including NV. Never really bothered with it.
But because first time round I sucked a fair bit in Fallout 1, it really helped. Unless you get shot critically in the face. That still hurts a lot, I seem to remember.
Tie between T51 and proper Advanced Power Armor. Dunno, I like the insect-like look of the APA. Somehow it feels very militaristic to me even though it's not really like any military gasmask.
Remnants armor and the cut Enclave Shocktrooper armor from New Vegas. Enclave armor is more advanced than anything the Brotherhood fields, so I've been using that in my present FNV playthrough. Normally, I stick to light armor. And the Shocktrooper armor is actually better than the armors that did make it into the final product.