We have a PS3 and love it. I think the graphics are better and LOVE the built in BlueRay player. I know the price of BlueRay players has dropped but I like that it's 1 less component I need plugged into my system.
If you want to do the sports/motion tracking games a lot I would probably go with the Xbox Kinect. We have the "Move" for our PS3 and we like it but it only tracks the wand.. my understanding is the Kinect tracks the whole body.
So............. for me I would rank them (For adults) PS3, Xbox, Wii and for Kids: Wii, Xbox, PS3
But hey, what do I know? LOL.