Wii U or PC. Or both I guess.
It is not like I only chose them because they are my preferred platforms either. I would buy a PS4 or XBONE if it turned out to be exclusive to either, but even if I had each platform I would still say Wii U or PC would be the better choices. For various reasons, but I think a good reason is that the games already available on those two platforms (Such as Mario, Kirby, etc. for Nintendo, and various indie games for PC) seem to match the style more so than the games of other platforms. As a result, those who own those the platforms are more likely to have interest in the game (not considering just long-time fans, but more so looking at obtaining new players for the game and the company to gain popularity). I am sure there may still be players who would be interested in the game who only own other platforms, but I believe the odds would be in favor of the Nintendo or PC player being more interested. I also think that a large amount of their original fans who are still carrying the torch for them would most likely own a Wii U. I suppose this is mostly guessing, but looking at the games on the consoles it seems pretty clear which one this game would fit in better with anyway.
Multiplatform is on option as well. Though I am not very knowledgeable about game development and all, but might that have some negatives involving the quality of the game? Such as optimization issues maybe? Or maybe just be too much extra hassle? I suppose as long as the final product is fine then I am happy with whatever they do.