(((interference)))
Veteran
Depends what you're going to do.
My standard class is silenced ACR with cold blooded and ninja. I started using that when I realized a lot of people don't care about harriers/pave lows, so why should I. The ACR has the advantage of being very easy to use. I've been able to stop knifers in some maps with very few shots in the head.
For CTF I use an UMP, lightweight, marathon and commando. On maps like Favela and Terminal that's a killer combo. You grab the flag and knife your way through to get back to your base.
For S&D I use the silenced ACR with the heartbeat sensor. Some players say it's lame, I don't care if it helps me finish the mission. I also use cold blooded and ninja, of course.
I play TDM/FFA at the moment, perhaps Ground War later on.
The ACR doesn't do a lot of damage though? Compared to the SCAR, I don't want to have to get multiple headshots to kill knifers, lol.