The only Kill based gametypes are FFA and TDM. Sorry sir, but if you're not playing the objective in an objective gametype you're doin it wrong.
But to level quickly? contracts. As many as you possibly can. And if you're really good, but want to exploit how the game works (do I even have to bring up your quote again) play CTF. For every kill you get while holding the enemy flag you get an offencive medal (effectively doubling the score for every kill you get).
3/4/5 killstreaks, with Hardline. Use SAM turret as it will get you points shooting down aircraft, care packages are good as well, you get points for throwing the marker and using the ks you get. Also, play Dom and cap flags for easy 150pts per flag. CTF is good if you run an smg class with LW and Marathon, as long as your capping flags. Demo can be good too, 500 pts for planting/defusing and the matches usually last a long time so you can really rack up kills and complete your gun challenges quickly. Don't stick to one weapon, try to use as many as you can for the challenge exp.
XBL: Frayedmetal Currently Playing: CoD: Black Ops & Chrono Cross
If you have a solid party, play HQ. I remember playing it with a party during the last Double EXP weekend, the amount of experience I was getting from those matches far outclassed what I was getting in other gametypes.
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I would suggest (as some of the other before me have already):
-Use Low(er) kill streaks with Hardline. -CTF is great way to rack up points and complete challenges. -Objective based game types (CTF, HQ, Domination, SnD, etc.) rack up more XP than your traditional Free-For-All and TDM.
BUT! I think it's more fun playing game types that you enjoy (DUH...) rather than playing game types that yield the most XP. Makes the whole prestige process less painless.
I'm out with that. Peace.
I was just a regular guy. My only super power was being invisible to girls.