It depends on your style of play, i personally roll ith the Thompson so in situations where i need a quick kill i can pop up. i also use a M9 alot of the time and depending on the map it varies what gun i wud use if u can email the map u prefer ill go into greater detial for you.
If you are playing hardcore I recommend using rifles with silencer or rifle grenades. Also use Overkill so you can carry more then one main weapon. Slight of Hand for faster reloading. Or UAV Jammer or Camouflage to be hide to be undetected by UAV.