Cod4: I didn't play too much of this game, as I only borrowed it for a brief time. I found myself using guns like the MP5 and the M1014 shotgun a lot.
MW2: Silenced Tar-21, or blinged with silencer and holographic. More ammo and higher rate of fire than the scar, great for CQC and long range with the silencer if you burst fire. It takes more skill to be accurate with the Tar-21 than it does the Scar. Even though it's my favorite, I found my try hard class to be one with an ACR with Acog, and stinger secondary, with cold blooded on. It was originally an anti-air class, but I found that I got exceptionally high scores with it.
Black Ops: I'm finding myself using the Ak-47 with dual mags a lot, though sometimes I'll just go around with dual pythons. I'm starting to use the Commando a bit, but just something about going to town with an Ak-47 is just awesome.