I have neither as I think consoles suck and much prefer a top end pc that is actually powerful rather than a console based on several years old technology.
However my brother is a gaming uber nerd and has owned the Wii, the PS3 and the Xbox 360.
Actually, he's probably owned about 4 Xbox 360's as like Amat says the failure rate is terrible. If you buy one it WILL go wrong at some point.
However for those who are tech savvy and dont want to pay for games the xbox is far better value as the machines are easily modded if you know what you're doing and you'll never have to buy a single game for it, unless you want to use xbos live.
If it bricks they can be fixed if you know what you're doing but it's a tedious process. My brother has literally had them held together with penny coins to stop them overheating.
The PS3 imo (only from looking at my brother's never owned one) is a far sexier looking device although I'm not sure it's as good for games. A lot of games when produced for both machines are better on the Xbox 360 for some reason. I don't know why this is but it happens a lot apparently, faster, better visuals, less slowdown.
But this is probably not that big a deal as the difference is hardly likely to be that great, certainly not as great as playing a game properly on a top end pc.
If you have money to burn I'd spend a grand or so and buy a decent pc myself. Get yourself a nice radeon 5870, (actually 5890's might be out now?) and a 24 inch widescreen monitor and enjoy proper gaming.
To be honest, my advice is totally wrong for most people, but as a life long pc customer and hater of all things console and Apple related I am something of a fanboy elitist

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