Simple question. I know we don't have all the info, so I guess rely on your gut feeling.

Contenders:

WiiU: Having terrible sales at the moment, but Nintendo always performs exceptionally well during the holidays and their heavy hitter will release around then. They also have a very loyal fanbase that is waiting for these titles. Plus there may be a price cut.

PS4: There seems to be real anticipation for it and it will probably have a very strong lauch line up, as well as much better 3rd party support than the WiiU. It may share many titles with the PS3 though and supply might be low. It's unknown whether it'll release WW too.

Xbox Whatever®: Similar to PS4, but taking into account that it might be a media box and have some sort of subsidized plan, as well as being popular in different regions of the world. Some negativity towards it now, but it may be forgotten by the time it launches.

If I have to choose I guess I'll go with WiiU despite its "doomedness", if only because the other two probably won't have too many consoles out there, and I think it'll have a decent holiday with the new titles and a price cut.

Assuming Mario Kart is out by then, it's likely gonna be WiiU.
Nintendo owns them holidays.

If not then we need to know more about PS4 and Nextbox launch titles.

Seriously though if Mario Kart is out by then it's gonna be WiiU.

Also assuming they launch worldwide of course. If I had to choose between the two however I'd go with Xbox and holidays are usually much stronger in America for some reason.

Next Xbox is my heart answer while my brain tells me PS4.

Probably Xbox because i think Sony is only going to launch Ps4 in America and Japan.

Xbox is going to win in the American territory and they might be able to make the European launch aswell as the American this year.

Wii U could probably pull off the win if they time a $50 price cut along with like a mario and like 2 other games since they are out in all territories

PS4

Nah, WiiU.

If only because it's launch-time for PS4 and XBox.

I personally believe the Nintendo Wii U will sell the most units during holiday season (October to December) because Nintendo will have Pikmin 3, Mario Kart, MarioU, Windwaker and they will actually Market the system. Nintendo is apparently doing a "re-release" of it.
N Wii U- 45% sales
PS4- 30% sales
Xbox 720- 25% sales

Depends on how much PS4/X720 cost, and whether Nintendo get Mario Kart/Smash Bros out in time for the holidays.

Knowing that the WiiU has an amazing holiday lineup and Nintendo always selling well in the holidays, and having no idea about PS4/Durango launch lineup or even it being 100% certain that they will release by the start of the holidays, particularly in Europe (and Japan for Durango), or how much supply will be available I would have to bet on WiiU.

Can't imagine how so many people think the Wii U won't beat PS4 and 720 this Holiday. It's in the bag.