Most always I use a class similar to this.

Primary: ACR
Secondary: Rangers/Models or Stinger (good XP when destroying killstreaks)
Equipment: Frags or Claymore
Spec. Grenade: Flash
Perk 1: Scavenger (always running out of ammo)
Perk 2: Stopping Power
Perk 3: Commando
DeathStreak: Martyrdom