Nightstalker definitely has the largest skill cap of the three. I would go nightstalker since if you are a skilled player, there's more you can do. Also run spike grenade, it's great if u are good with it.
English
-
Nighstalker is by far the easiest because it has a great neutral game, gunslinger is by far the higher skill cap because it's dependent on your gun game not how many nades and smoke you can spam. [i]~ Nyahh! =^,.,^=[/i]
-
It doesn't really have a good neutral. Its grenades suck, and there's not much utility for the smoke bomb in PvP, in my experience. I'd pick Gunslinger over Nightstalker because you can't rely on your abilities as a way to kill.