I have all the consoles.
PS3 - gets used very rarely. A couple of times a year...
It's the original one with backward compatibility, so I'm hesitating on selling it!
Wii - Great little machine when friends are around... Other than that, it also just gathers dust.
360 - Use this the most. Excellent online play, and can keep in touch with friends back in England. It's the only reason this is used the most. If it weren't for online play, it'd be used less than the PS3.
As I'm no longer a "gamer", I think my vote goes to the 360 simply because of online gameplay.