I use a few different ones
Marathon, Cold blooded, and ninja with a silenced M4 or any assult rifle really i also some times use the EBR
Some times i swap marathon for bling and use a silencer and heart beat monitor, its pretty useful for finding campers, it seems not many people use ninja.
Another good one is to use Marathon, Lightweight (or what ever that one is called that makes you fast) and commando, with somthing like the UMP45, this one allows you to move up on the campers really fast. Often they wont see you and even if they do they cant hit you because you are simply too fast between cover. You get lots of knifing oppourtunities with this one
Watch your kill screens and remember where they are. Oh and at times the javelin is really useful, it can target an area, so if you think there is a camper in the distance on top of a building or somthing lock the javelin on to somthing near by and let her rip! Its almost like having a predator missile all the time!