This year? GTAIV

Lifetime:... I won't predict, don't want to eat crow

Wiifit will win over them both separetly and combined by the end of this year.

Only time I think we will see GTA win over wiifit is now theese first months of launch after that the world will belong to Wiifit and Wii.

i think wiifit will sell more than the wii, 360 and ps3 put together, it may not reach the ds however.

short term WW GTA IV , long time WW Wii Fit. Although both games are going to be monster sellers.

wii fit. . . itll sell forever

GTA IV, this year and lifetime by a good margin.

I believe that Wii Fit will trump both versions of GTA IV this year. Only because it is more accessible to everyone (and their grandmother) whereas GTA IV is rated M (not like that's stopping anyone from purchasing the game for their little bros =P).

Imagine how many copies Wii Fit will sell around launch date and I imagine it would have tremendous legs leading up to Christmas and onwards. SSBB was released just a couple months ago and has already sold more than 3 million copies here in America alone so Wii Fit shouldn't have any problems surpassing that amount. You also have to take into consideration that the software is being sold in three different regions compared to GTA IV currently on sale at two.

Lets not forget what could happen if they also showcase the software on Good Morning America as well. 

Hum that is an interesting question. Wii Fit has an advantage in an earlier release, and a serious advantage in very respectable Japan sales. Still it is uncertain how many it will sell lifetime, and GTA has a history of being one of the best selling series ever. I am going to say Wii Fit can beat either consoles version but combined they will beat Wii Fit.

GTAIV for both consoles will be more at first but if the wii fit is like the wii and selling out every week, then it wont take long for the wii fit to take over gtaIV for both consoles.

And who knows, wii fit could be the next wii play.