All those are great choices.

I think Fast Racing Neo could win here because all the next gen stuff is moving with an almost perfect 60fps, the resolution is not that good though. But Xenoblade Chroniclex X looks impressive for a game with such a gigantic scope and seems a great achievement for the console, it really looks like something impossible to achieve on the 7th gen.

However on both games you can see flaws and limitations, even if they look great, but on games like Captain toad or Yoshi's Woolly World, the graphics are close to perfect, as they fullfil their respective ambitions and hide any hint of hardware limitations.

Dunno, i think they are all great showcases for different resons, but FRN and XCX are probably the best ones.

Played all of them and I consider X is the game has most outstanding graphic on Wii U

Absolutely love the environment in Xenoblade Chronicles but overall, I think I have to go with Yoshi. That game is definitely beautiful. A bit surprised with the lack of votes it has.. I think it looks better than the other cartoonish games.

I voted NFS because it dispelled the myth of WiiU being weaker than 360/PS3 and that you could have both gamepad features and gorgeous environments.

Until Zelda arrives it's between XCX and Bayonetta 2.

My thought aswell 

Super Mario 3d World looks phenomenal

Mario kart 8 gets my nod. Looks great in motion too, whereas Fast Racing Neo looks pretty messy when moving.
I haven't played Xenoblade yet nor Bayonetta, can't judge them.
Pikmin 3 has great artwork, Super Mario 3D looks great as well.

Technically Lego City Undercover was most impressive. Large open world, no bugs, how is that possible.

Xenoblade looks like a 2008 Xbox 360 game and that's being generous. Don't let the videos and screenshots you like they did me. It only looks good running on the GamePad.

While I've only played two hours thus far, I have to agree with this sentiment from a technical aspect.  You have to give a lot of "well the world is so big" concessions in order for this game to be a "graphical showcase".  

It's only as bad as if you're looking not too far the game's models, my screenshot ingame, open image in new tab on your browser for full resolution