Wii will sell the most as it's a new system with some very attractive launch offerings, the novelty factor will be there in abundance, its target audience is vast compared to the PS3 and 360, it's cheaper than the competition, and it'll have well over 1 million units out at launch, with in excess of 4 million units out by the end of this calendar year.
Next up comes 360, with its already-established installed base and a plethora of top titles out this autumn and winter. Its online service has a great rep, albeit one scarred by stupid people, it's a whole heap cheaper than the PS3 and its games look just as good (for now...).
And lastly comes the PS3. The main reason for it being in third place here is the fact that only a measly 500,000 units will be available at launch, with a projected 500,000 more by the end of December 2006. Even the DS Lite may be able to outsell it. Still, it'll sell out, though obviously this won't be enough to propel it to #1, what with the severe lack of units and all. Oh yes, and at that price it isn't going to attract anyone other than tech junkies and early adopters anyway.