At this point, who knows? Last generation the answer was MO POWA!! But historically that's never been the answer, nor has coming out of the gate first.
I think we'll have a better idea when MS and Sony show their hands and Nintendo tells us more. We really don't know anything right now. We don't know how powerful the Nintendo console is, what the price is, when it will launch. We don't know if their controller design will be copied. We don't know if Sony will go for a dualshock 4, if the next xbox will come with Kinect or do something completely different.
At this point we don't even have much to base a guess on, but even the past actions of these companies have shown all of them have an unpredictable streak.
Who ever makes the best balance of power and affordability, the best controller, and who has the most interesting exclusives will most likely determine it.
Keep in mind too 3rd parties have no loyalty anymore, so it could very well be 33/33/33 or some variation close to that with the groups made up people that prefer the controller or specific games.
3rd Party Wall of Shame
http://www.nintendoworldreport.com/forums/index.php?topic=30478.msg581036#msg581036
