These predictions aren't based on real statistics but they are a probable guesstimate.

There are 3 main gaming markets on our planet.  North America, Europe and the Far East.

In Europe the most likely console to win is the PlayStation 3.  This is merely because its a trusted brand amongst the casuals there and they aren't too bothered about spending a hundred more for a console with more power.

In the Far East the Xbox 360 hasn't got off to a good start.  Wii and PS3 are still in the running though.  PS3 offering RPG-ertunities which they love so much over there.  Wii offering a new style of gameplay which will definately attract people who are tired of the status quo of gaming ridgedly fixed between the physical barrier of a d pad and an analogue stick.  I think that the Wii will just clench it on the sales front.

In North America the consumers aren't product loyal so its a fresh start for next gen.  Xbox 360 is very popular already there.  360 is a good leeway between Wii and PS3.  The Wii will have a large following here, as will the 360.  And with the prospect of a Wii and a 360 possibly costing the same as a PS3, Wii360 might be the deformed mutant of North American living rooms.

All of these consoles depend on other factors though.  For example:  if people don't take well to the Wii it'll be laughed off the shelves.  Or if HD-DVD flops, fuel to Sony's fire of superiority with Blue Ray.  Or if consumers stand up to Sony and say "£300/$499!!!!  What you talkin' boout Willis?".