I own a 360 and my girlfriend owns a Wii, even though I play both. My time is probably spend 90-10 toward the 360. Since most of my gaming time is alone and I like FPS, I end up on the 360 so I can play online with friends. It's so hard for me to go from the 360 where everything looks and sounds great to the Wii where it looks like crap on my HDTV with only stereo. I do enjoy Mario Galaxy, but sad to say, the graphics always pull me out from the game. And, I know I am not the norm, but I really can't get into the Wii controller. I know I would personally love Mario Galaxy so much more if I had a regular controller with joysticks instead having to move my hand all around to get the stars and attack enemies. Not that the 360 is perfect, I just got mine back a couple weeks ago from being repaired.
My friend just got a PS3 a week ago, it is really starting to come around since launch. Lots of good games coming out for it now and the system is really starting to show its potential. If I had to choose between the 360 and the PS3 now, I would probably go with the PS3 just because it is a much better value.