Probably the 360. It's not hogging the downstairs TV and is connected to an old PC monitor in my room. The Wii and PC are joint (I don't have that many decent games for both)
PS2 ... Oh, wait. That's not a choice. Then it's the PC with it's delicious assortment of emulators. I play all my store-bought GBA games on an emulator. Less neck strain and less eye strain.
I'd say pc but mine sucks so I'm going with my good friend the Wii on this one. PC has been a downer since ever game I buy give my the blue screen of death. If only I had that gay Bios upgrade I would have that damn problem.
My only choice is the 360. This comp I'm on is almost as old as I am. Maybe I can run Jetpack on it. I do have a nice over-clocked comp back home, but that was used mostly for photo editing and torrenting.
I'm still hoping to be able to buy a PS3 of my own when they restock on the MGS4 bundles sometime this month, as for now I'm playing a lot of games on my neighbor's PS3 because they are nice enough to let me.