With WMX installed and on a crit build it's either the Paciencia or the Gobi Campaign Scout Rifle for me. The latter silently pops heads while the former has the same crit damage as an AMR, murdering just about anything from a safe distance.
Without WMX those aren't as good, since the Paciencia cannot have a scope and the ironsights are misaligned while the GCSR doesn't fit a silencer, making Cristine's COS Rifle the better choice.
Other than that, the Ratslayer is great up to the midgame because of the constant silent crits and Blood-Nap is a great looking knife which deals tons of damage.