I think it all boils down to a matter of personal preference. I personally like CoD over Halo because I like how one or two bullets to someone's chest kills them as opposed to an entire clip of ammo. Don't even try calling me a noob because I say an entire clip, because for the most part it's true :P

In my book, Call of Duty gets my vote for its more diverse gametypes and more sophisticated multiplayer system (leveling up, perks, etc.)