That's a really tough question!
Firstly let us take a look at Wii Fit Plus. Now Wii Fit Plus is going to be taking over from Wii Fit as the pack in game with the balance board. It will also be offered as a stand alone title at a budget price. This means two things:
1. Whatever momentum Wii Fit has in the lead up to the launch of Wii Fit Plus will carry over to Wii Fit Plus. What I mean by that is anyone wanting to pick up Wii Fit and hasn't done so will automatically pick up Wii Fit Plus once it has launched and therefore it will be guaranteed to have legs.
2. Because it's being offered as a stand alone title, everybody that already owns Wii Fit can upgrade to Wii Fit Plus. Now if it was full price, I would have guessed that around 33% of Wii Fit owners would have upgraded. At a budget price I can imagine somewhere just below 50% of owners upgrading to Wii Fit Plus.
So by mid October Wii Fit should be standing at sales of around 22.5 Million. This means that around 11 Million people should upgrade to Wii Fit Plus. Not only that but Wii Fit's momentum will carry and I think another 8 Million or so people will buy it.
Wii Fit Plus = 19 Million copies sold
Next let us take a look at Wii Sports Resort. For this one, I would like to use a picture:
Wii Sports Resort seems to be trending very similarly to Wii Fit when taking into account the boost from the launch in Europe and the Americas. It also launched in the slowest period of the year, comes with a Wii Motion Plus, but is cheaper than Wii Fit was.
With that in mid, I expect Wii Sports Resort to hit somewhere in the area of 24 Million sold by the end of it's lifetime.
Finally, New Super Mario Bros. Wii.. I think this one is going to outsell it's DS brother just like Mario Kart Wii has outsold Mario Kart DS. I think the fact that it's a 2D Mario platformer using the Wii Remote in a very easy to understand manner but with a couple of motion controlled twists along with the HUGE addition of multiplayer cements this game as a 10 Million+ seller. The real question though is how much more than 10 Million can it get?
I've done a full analysis in another thread and I basically ended up thinking that New Super Mario Bros. Wii will sell about 22 Million copies
So in the end it's going to be:
Wii Sports Resort > New Super Mario Bros. Wii > Wii Fit Plus
24 million > 22 million > 19 million
