360 due to the SHEER amount of games available for it both old and new.
And how about all these great double acts..............
2 Gears of war games, 2 Forzas, 2 Condemneds, 2 Project Gotham Racings, 2 Halos, 2 Saints Rows, 2 Dead risings (Well, when Rising 2 hits early next year), 2 Crackdowns (Again from early next year), 2 Left 4 Deads (the ban in Aus will get lifted)
Plus great games on the way like Splinter cell: Conviction, Alan wake, Fable III and so on.
And XBLA is second to none in the arcade department (A new game released every week GUARANTEED, sometimes 2 or 3 games a week)
Purely from a games point of view 360 easily wins.