Well, I have a PS2, PSP, Xbox, and an Xbox 360. The Xbox I got used, (I only got it for Halo) and after about 6 months it wouldn't recognize the discs. My PS2 and PSP still work fine, but I did buy them new. I just bought a 360, and I love it. Gamerscore is nice, it's kind of a pride thing, and you get a sense of accomplishment. The graphics are wonderful, for example, I have all the Lego games for the PS2, and I rented Indy for 360, and it has more texture and more defined figures. Xbox LIVE is 50$ a year, and well worth it in my opinion. I think microsoft points are stupid, just use real currency like PSN. And there are so many good games for it, for example GTAIV, Halo 3, Gears of war, Left 4 Dead, and many more.
Several of my friends have Wiis, and I do not like them. The graphics are worse than the PS2, and the motion control is anything but accurate. Plus, almost all of the games are family friendly, and not good for a hardcore gamer.
I've never played a PS3, so I can't say anything about it.