I am voting for the X360. If the Wii wasn't so disappointing on a HD TV and if I had not been disappointed in Super Mario Brothers Wii and Monster Hunter Tri, it would probably be my only system.
The PS3 has Blu-ray and a few exclusives I would like to play.
The Xbox 360 has many of the same games - and they usually look better despite the system being older. And I think Kinect is the future of gaming. I like odd/exploring type games like Alan Wake (X360) and Endless Ocean 2 (Wii).
I like Major Nelson and the other shows informing me about new stuff and how to use the stuff I already have.
Plus, and a big plus, is I can demo almost every game and play a little bit of it. Sometimes that's enough - I read about a game - think "oh, I want to try that." Get the demo, play it, then buy it, or wait until it goes on sale, or be happy with the demo.
I know you can download some demos on a PS3, but every time I’ve tried to do it a friends house it takes forever.