well, this is a class i used to use when i was playing SND when i was defending:
FAMAS with Holo and FMJ(just to make my aim better, so i can kill with only 1 burst and not missing anything)
PP2000 or G18 with Extended Mags and Silencer, so whenever i have to change positions without alerting anyone or when someone gets too close to me.
Perks:
Bling Pro
Stopping power or sometimes even Coldblooded
Steady Aim or Ninja PRO
Stuns so i can stun people and defuse the bomb
Semtex so i can throw a grenade if i see someone camping/plantin the bomb
Hope this helps???