I'd have to say Call of Duty: Black Ops II. Mostly because that is the first one I played. Ghost is OK, the lag and campers are worse than on Black Ops II.
I would have to choose call of duty modern warfare 3. The maps were well latex out and the gameplay was fun and awesome. I spent many hours playing that game.
I loved cod 4 as that is where I started but bo 1 was great. Wager matches were better than any other cod game and zombies moon map was so great. So bo 1 was the best for me even though 4 is right behind.
Personally I like Black ops II. Mainly because I am good at it. The graphics weren't that great and neither were the weapons, but some of the maps were awesome!
MW3 or MW2
AW is catching up but I'm not committed to calling it my favorite.
lol and yet were still waiting for someone to favorite call of duty ghost hahaha