Xbox 360: Count all the 360 games that are 'truly' exclusive - i.e. not on PS3, not on Wii, not on PC. How many are there? Are they worth it? Me, as I also have a gaming PC, do not want to spend a few hundred bucks on a console just to be able to play Halo 3, Gears 2 and Viva Pinata. Live is a good system, undeniably, but it still doesn't beat PC online functions.
PS3: Heavy Rain, God of War, Metal Gear, Infamous - these are games you don't get on any other platform. Also, there's blu-ray, which is a plus as soons as the fucking discs get cheaper (30 bucks for a movie, jesus...) Downside, I've heard, is the online part - don't know whether you friend cares about that. I don't, for online multiplayer I have my PC.
Wii: There ARE some good games out there on this platform. Resident Evil 4, Zelda: TP, Mario, Metroid, Okami, No More Heroes, House of the Dead, Mortal Kombat, Dead Rising, The Conduit (there are more but I think you get my point). If you use the console as a kind of 'secondary platform', like me, you'll be happy with it. The controls on those games are perfectly responsive, too.