I sorta think that both Wii and xbox 360 are going to succeed. The two don't necessarily have to compete against each other, coz in my opinion they seem to target at different market segments- those who enjoy a new way of gaming and those who prioritise the audio and visual experience. The two consoles have very different advantages that will attract different audience. Personally I like both. But because of the fact that PC can be a close substitute to 360, with modding capabilities despite the need for upgrades, if I was ever to buy a console perhaps I'd try Wii. Without PC in consideration, 360 would be my choice- graphics is still the most important criterion for me.
While I see some of us here said that only the Wii is a next-gen console, because of its innovative gaming capabilities, I do not quite agree. No one said that a next-gen console has to offer a completely new way of gaming. The fact that the graphical abilities of xbox 360 and ps3 has evolved greatly compared to the current-generation machines could qualify them as next-gen. What I'm getting at is that there isn't a real definition for "next gen" gaming consoles, thus one shouldn't rely on it to decide which to buy. Ultimately, it should be the customer's own needs that are the deciding factors.