here is what i prefer. Remeber, modify these classes everyone is suggesting to fit your own preferences.

RunNgun (general combat)

P90 red dot sight

USP silenced (best pitol imo- minimum recoil, same dmg as the other 2 "small" pistols. Desert eagle, though powerful, has too much recoil, and only 7 bullets per clip)

x3 flash (toss in a building in which there is an enemy camper / in a better postion then urself)

stopping power (kill in one less bullet)

steady aim (always hipfire in CQC)

Stealth

MP5 silenced

M9 (shares amo with MP5, so a little like bandolier)

x3 flash

UAV Jammer

dead silenced (lets u creep up on smart bats, i find steady aim isnt really required to hip fire successfully with the MP5)

Search and Destroy

M1014 (semi-auto shotty for close quarters)

M4 carbine, silenced (for long range)

stun (if i get an "X" marker when i toss a stun in a room, i know theres a stunned enemy inside. so i just toss a nade in, and BAM he cant get away lolz)

clamores (usefulness goes without saying really in this game mode)

overkill (uhhh.. duh obvious)

dead silence (stealth is extremely important in this game moed, as only 1 life per round)

I average around 8-15 kills per round with that class, and win the great majority of my games, as long as my team doesnt entirely suck lolz.

Domination

whatever gun i feel like using

USP silenced

stun

C4 (place on flags, when it is announced u are losing the flag, double tap square to detonate)

ur choice

ur choice

really only important thing in domination is C4 to guard flags xD