Ever since retiring the Executioner and picking up the KAP-40 as well as doing away with the Combat Axe in favor of C4, I've had some success with the following class. I started out playing Black Ops 2 thinking that getting a Swarm with an Assault Shield class would be a significant achievement, but a few days back I managed a double Swarm and now tonight a triple. Works best in a gamemode like Domination but had some good games in Kill Confirmed and FFA too.
Assault Shield KAP-40
Flak Jacket, Hardline (Perk 1 Greed) Scavenger, Fast Hands (Perk 2 Greed) Tactical Mask (Can be swapped out for extended mag or Engineer if you use Care Packages)
Riot and Assault Shield Gameplays and Montages: http://www.youtube.com/mitchacho