Black Ops 1 for the utter garbage connection in most games, never has it been so bad. The hit detection was atrocious. To top that, the game was ridiculously unbalanced, and they introduced ideas that they were even ashamed to bring back in the sequel (COD Points). BO1 is the abortion of Call Of Duty games.
Right behind it though is MW2, only for the incredibly stupid perk system with one man army and such, as well as akimbo shotguns, danger close grenades, and so on. The dev's must of been high, or just downright Blue when making that game.
Ghosts can easily get out of the shitty COD games category by nerfing the dog, removing danger close, and fixing spawn issues. Other than that, it's quite enjoyable.