Get the Wii version if you can find it for a decent price, it seems to be superior in every way, but if you can't get your hands on it then go with the 3DS version.

Well I just bought the wii version last june and it is freaking AWESOME!
The 3DS version probably has worse graphica, judging from the videos, but never forget that all 3ds games look worse in the videos and the 3D effect increases the resolution.
Dont put graphics in ur mind a lot, cuz it also looks bad on wii. The artstyle is good though.
To answer ur question, I am ali more of a handheld gamer, so i will sell my wii copy and get the 3ds version when it comes out.
Dou love ur wii more or 3ds? Thats it :)
3DS version FTW!

The 3DS version, because it has more shader cores and more everything across the board.

Both versions are pure cell-shaded graphics, but the 3DS has the best cell-shaded version of graphics because it can afford to make the cell-shaded graphics more cell-shaded looking, because it has stereoscopic 3D which will make the graphics more three-dimensional looking then the Wii version cell-shaded graphics in 2D.

At least wait for 3D screenshots of the 3DS version, before you make your judgement.

Plus the 3DS version is also the Definitive Version with stuff they haven't even mention yet, that are exclusive to the New 3DS version.