That is debatable on what you look for in a gaming console.
360 (If you want a classic amount of 3rd gen games that are fun and look really good)
Wii (If you like interactivity and games that don't follow the norm)
PS3 (If you need the latest and greatest and don't mind paying top dollar for it)
Personally I own a 360 and will have a Wii when I get back... I will be waiting til next year when the PS3 is more fleshed out and has a library of games that are worthy of even playing for me.
I am going for a 360, cheaper than the PS3 and at the moment looks better than it. Wii looks great but I am going to buy Zelda for gamecube and wait a while.
get teh 360 now, wii after you've played it and are sure you like it, and the ps3 next fall, when it'll actually have games that look better than on the 360 and it's ps3-only titles will be worth shelling out the 600 for it