That's a tough call, obviously microsoft is winning right now. I know the ps3 will not get as many sales as sony predicts at launch due to the $600 price tag, however over time(price drops) i think it will sell better. I'll bet money that the wii will sell out on launch date because most people want one and it's so affordable, it will be the first one i get. The 360 has somewhat of an advantage right now since it was released last year, a year before the other two, but i don't think it will be number one.
I can't really make a prediction yet, but i know this time around nintendo won't be in last by a longshot. Here's my guess.
ps3 either coming in 1st or 3rd
360 coming in 2nd or 3rd
wii coming in 2nd or 1st
here's a possible outcome if the ps3 actually sells
ps3 1st
wii 2nd
360 3rd
or if sony screw themselves over like some think
wii 1st
360 2nd
ps3 3rd
You probably think i'm a nintendo fanboy now, but i just think the wii will outsell the 360, and maybe even the ps3.