I enjoy either the UMP45 for the accurateness and damage, it has poor fire rate, but I can simply just add Rapid Fire to increase the speed, and Extended Mags to make up for lost ammo from the Rapid Fire.
Or, I'll use the P90 Silenced, so people won't see the rush. It pretty much just a natural good gun, but I always use Specialist on it, It's my personal MOAB gun. I always get 18+ Gun Streak on it.