The sales should be better since Skyward Sword was released at the end of the Wii's lifespan. But we don't really know all too much about the new Zelda nor do we know much of how well the Wii U will perform.

There is too much that we don't know.

WiiU Zelda. Why?

1.1st one on the console (Come on WW remake doesn't count)
2.SS needed WiiMotion+. Big turnoff.
3.Personally know 3 people that didn't get it because they didn't want to buy another Wii, after theirs broke or they traded in. Such is the near end of a console gen.
4.Dolphin emulator made it so that you could just emulate a copy. WiiU won't be cracked that fast, at least a Dolphin WiiU won't exist by then.

WiiU absolutely.

Why?

First Zelda in HD AND for the console, will release during Wii U peak year, and it will be made in less time.
Gameplay features are yet to be determined, but the economical and market environment the Wii U will be at lends itself better to the game selling 5 million+.

Dolphin was a problem. People rave about how the dolphin emulated game is so much better than the original.

Wiis have broken over the years. Just that the failure rate is low compared to the HD twins.

Motion control? Hm.....I honestly don't know. But SS already showed Zelda maximising the input potential of the Wii, I'd like them to focus on the gamepad instead this time. Motion control remote was for the Wii. WiiU should be gamepad focused and a Zelda game that focuses in on that is what i want.

Def the wiiu version since ti wont need an extra piece to play it and it will be released earlier in the consoles life...wait that doesn't make sense in a way lol.

I think Wii U will do better. The novelty of "HD Zelda" will attract people the way the novelty of "gritty Zelda" attracted gamers to Twilight Princess. Skyward Sword also required Motion Plus, which limited its marketability; the fact that all Wiimotes sold in the past few years have had Motion Plus built-in will help make the accessory... well, less of an accessory.

Wii U.

The Wii U Zelda demo from 2011 was far better received than the unveiling of Skyward Sword for Wii.

Yes, I know it's just a tech demo and not indicative of the actual game but it's the nature of having an HD Zelda during the system's early years that will draw the crowd.

Twilight Princess sold so much better than SS. Largely because it was early in the system life, it had an art style that appealed to gamers and it was playable with the default control system.

Wii U for sure. According to the several Zelda fans I know, the MotionPlus requirement was a barrier from them actually purchasing the game. I've loaned out Skyward Sword and my spare MotionPlus three times in the past year. Kingdom Hearts 3D twice. Now I'm getting three different requests for Xenoblade.

I need to stop this and tell them to actually pay money for a game they want to play.

Now we know why Skyward Sword didn't sell.  Because you lent your copy to everyone.

STOP KILLING NINTENDO!

I blame Call of Duty. None of my friends listen to me when I say "you know if you skip just one of the annual Call of Duty releases, you could buy another game and not miss out on anything whatsoever".