Depends on the game really.
For any game that is best played with the Xbox 360 controller (Racing,GTA4,Street Fighter, etc) I prefer my 46" Samsung TV at 1920x1080. It looks much more stunning and immersive than my 22" monitor, and lying on the sofa is so relaxing.
For high accuracy mouse+keyboard games (CS:S, CoD, L4D etc) I sit at my desk with my Samsung 22" 1680x1050 monitor.