If you can aim, sniper rifles. If you can't, shotguns. If you are really good at spray control, rifles.
Shotguns. Has the browning auto, which has the accuracy of a sniper, the damage of a shotgun, and the fire rate of an AR/SMG.
The GS3G1 is always going to be my favorite weapon. The closest second is the Galil. 3rd is the Silent FOX.