My "opinion" is they are all good in thier own ways.
You want a serious gaming machine, X-Box.
You want a family or party machine, Wii.
You want an entertainment system, PS3.
Being a more casual gamer and a serious movie buff, PS3 was the only choice for me. My best friend on the other hand is a hardcore gamer, so he owns the 360 and Wii, and though he says he loves them both equally, he plays the 360 about a thousand times more than his Wii.
If I had to choose, I'd say Wii just because I don't want a work-out, I just want to relax. Plus it's got the worst selection of games, especially since I don't have children to play it with.