Tie between Wii and 360 - 360 for the XNA Game Studio that I can eventually use my c# skills on (ya, I don't have much for skills, but I'm always willing to learn), Wii for Trauma Center Second Opinion.
PS3 costs too much and doesn't have GTA as a strong point anymore, and it isn't getting Guitar Hero 2 - didn't launch in time for it, my ps2 is still gunna be geting some use.
I'm not starting the whole ps3 sucks debate thing, I just hope blu-ray doesn't turn into the psp's umd - universal media disc that's only playable on one system, thereby making it exclusive, not universal.
Personally though, the whole next-gen debate is all BS. I've heard the arguments on both sides, and heres what I have to say:
PS3? If you got the cash, go for it. Have fun. I can't afford it, and neither can anyone I know. Puts things in perspective when my best friend works in a hospital and rakes in more than I could working on entry-level COBOL (there's job openings for entry level cobol programming at 80k a year)
Wii? If you need a cheaper system that may very well get some kickass party games (excluding brawl which isn't a "maybe" but a "when"), start grabbing. Even WiiSports is supposed to be pretty cool.
360? It's been out a while, which means there's already a base of people for online play. It also means the game library's open for business. XNA GS is coming out soon (theoretically), which gives us freelance developers some hope - c# for the win!
Wii60? In my opinion you got good taste - you're grabbing probably the most unique system available, and the one that's already got online gamers and a good game library. Costs $50 more than a ps3, but you're getting two systems. Makes it easier when great games come out - you got a decent chance of it being on one of the two systems you have.
And now for my minirant: Remember the whole "ps3 controller doesn't have rumble" thing? I'm curious what the hell's using up all the power then. The ps3 controller is reported to last 30 hours. The Wii controller is reported to last 30 with a speaker on the front, the audio, the accelerometer functionality on, and the pointer on. Huh.
Edit for above: I might get one, but that all assumes I stop spending money on games for pc/wii/360 first. If the flow of games I want doesn't stop, I won't be grabbing a ps3 any time soon.