demolition can be big if you are up against crappy players, you can get 50 kills without breaking a sweat..... that being said, domination can be huge if you get a lot of capture kills (200 pts per kill and 200 to cap flag, could be 800 points on one flag capture no problem. kill confirmed, however, is the generally accepted xp mode --- Now Playing: Black Ops II Playing Soon: Dishonored, Halo 4, Walking Dead, Hitman, Rage, Need for Speed
Anywhere between 6000-8000 for a 20-30 kill game. Only 5 minutes long. Plus if you use a bunch of tokens to unlock as many weapons as possible you will unlock camo/attachment challenge XP on weapons you wouldn't normally use.
Not unusual for me to come out with 12-15k sometimes whilst having a lot of fun in the progress.
Dom with the right scorestreak setup, KC, and league are all good options. Also using a lot of EMP grenades is pretty boss for xp. They hit people through walls and floors, the effect hangs around forever, and they give a nice assist bonus in addition to xp from destroying streaks and equipment.