The best class for level 14 is a sniper. Get the best sniper (preferably the third) and the best secondary with the crit mastery. Go around headshotting until you're out of ammo and then shoot with the secondary until you die.
I played as an Assassin-Rouge character. The beginning was a touch difficult but after the wolves it turned into an all out rape-fest. I killed the final boss naked with just weps, nerfing needs to be done.