I like all game modes. My favorite is hardcore on dome. What I really wish they had in BO2 is team tac. The game mode was really cool when u just wanted to play every game mode.
Hardcore is the only way to go, and of course TDM is my favorite. I'm always game for some 1v1, 2v2, or 3v3 given I have good teammates that communicate. I'll occasionally play KC and/or DOM - but I hate every other mode, especially S&D.