I have to say that, world wide, I don't think 360 will be the champ, but I do feel that it will have the most support. From now until Fall, the only notable releases for Wii are Super Paper Mario, Super Mario Galaxy, and Fire Emblem (and that's not even popular in terms of sales outside of Japan).
360, however, will hold a lot of influence. It's got the niche games that appeal to gamers like me (Earth Defense Force, Culdcept, Viva Pinata;etc.) while still maintaining a wide variety of main appeal games to casuals (Madden, GTA, Halo). I think that 360, like ps2, will be quite popular with gamers as a whole, and will continue to hold a good amount of titles, making it about even with Wii on the world wide spectrum, if not slightly below it.
The thing about Wii is that, how do we know if the masses won't get bored with Wii? I may be the only thinking this, but I think that after this year, people will get bored with Wii and it won't grow as much due to lack of games, much like the Gamecube.
I may be underestimating the main masses in this gamble, but I think that the GAMERS around the world will be able to keep 360 afloat just as much as non gamers will keep Wii afloat.