I'll go with OG Xbox.
360 might have improved online multiplayer and the socializing aspect in the console space - but I had more fun with the competitive and cooperative nature of the OG Xbox. A lot more good games to play, first party and third party - compared to just Halo, Gears, COD and Bad Company 2 on the next generation when it comes to this space.
Even though OG Xbox had the luxury of a short life-span - the 360 was only actually strong for half a generation.