Mine would be GTA4. I loved the online functionality of playing with multiple friends. So much fun, mayhem, rage, etc. It was a blast. I can't wait to do that again in GTA5.
Runner up would be Saints Row the Third. First Saints Row game I've ever played, and I loved the craziness of it. I hope the developers the best of luck with their new publisher. --- Official Aquaman & Deathstroke of Injustice Gods Among Us