For all around defense, offense, get yer kill streaks you need? ScarL, Grenade launcher attachment, Silencer attachment, steel sights only, RPG Secondary,

Perks: Slight of hand (load fast) pro, Stalker pro, Marksman pro or steady aim pro.
Defense: any shot gun azz hat runs near you use RPG to get them "all blowed up". Silencer allows you to stay off radar and stalker keeps you off map completely - no "knife/shot in the back" scenarios.
Offense: anyone u shoot 3 times and then they run around a wall half dead> shoot grenade and finish them off. Anyone holing up in a room or when playing Domination will eat an RPG for a multi kill.

Death streak: last stand
Scar/silencer is extremely accurate yet has some power and a gd fire rate.