Story: World at War - what a story in this game. Amazing end to the "repetitive" world war 2 setting for Call of Duty. Much memories.
Multiplayer: Modern Warfare 2 - tempted to put in all around best COD, but falls short a bit. Honestly I've never sunk more hours into a multiplayer game besides super smash bros. Great online play.
All around best COD: Modern Warfare 1 - Oh god what an amazing game. Anybody who doesn't think this is in the top 1 or 2 COD games is crazy or stupid. Set the multiplayer of the decade.