I've been using Silenced Scar, Magnum with tactical knife, Marathon/Scavenger, Cold Blooded and commando.
Your very stealth and stay away from your teammates, basically stay away from where the action is, and if the enemy gets a UAV and your within 5 feet of you teammates chances are yu'll be spotted. I tend to run around and stab 4-5 people before i even start shooting, if you can get 4-5 knife kills and 2-3 kills with a claymore/semtex/silenced gun then your golden. now call in your harrier and continue running AWAY from the action, watch before you run around a corner and always be ready to stab somebody.
Chopper gunner is self explainatory, usually ill try and stab one or 2 more people before i call in the chopper gunner, on my way to a great hiding spot so you dont get killed while controlling it, if you have scavenger you should pick up extra claymores around you so they cant sneak up on you. By the time the gunner runs out you should hae a nuke... if not hide in a corner and stab somebody when they run by.