This is strange to compare now. Having said that, guess what my answer regardless of anything would be...

Witcher 3 since we know nothing about Zelda U.

they changed the artstyle for the new dlc on witcher 3 which make it similar (not same) to zelda u/skyward sword.

Watch this trailer:

Zelda Wii U 

Sure witcher is still more realsitic and co, but both game share similar color tones.

Haven't played either. Even though Zelda U looks very promising, I don't like 3D Zeldas that much. So probably The Witcher

"Both similar Artstyle" um, no. The Witcher has milfs and titties so it wins by default.

Blood and Wine looks more like the Fable 4 we probably never will get.
Xbox is last on the list of consoles that I consider buying but for something like Witcher/Fable I would be very interested.

As for Zelda U/NX: You never know what a new Zelda will be like until it is released. The games are always "different" although at the same time very recognizable. I just hope that there never will be a dark, gritty, realistic Zelda.

They didn't change the art style at all. They changed the color pallet, and even that is a stretch. It's just a setting with more primary colors in it. It looks absolutely nothing like Zelda U/NX.

And for the record, SS and ZU don't have a similar art style, either. It's just the color pallet that's similar.

It looks very similar to me. If you dont agree, i probl cant change your opinion.

You're wrong. Art style isn't opinion. If I draw a stick figure and say "this stick figure has a similar art style to Zelda U to me," that's not an opinion. I would be wrong. You're comparing two things with objective properties. Your conclusion of the similarities of those to properties are not subjective. They either look similar, or they don't. In order to look similar, that have to have most things in common. They have absolutely nothing artistically in common outside of setting. Not even the color pallets are the same. Not an opinion. You can take a survey of the numerical value of the colors used and compare the two.

Just because you feel something doesn't mean its an opinion. If there's a blizzard outside and you say it's raining, you can't back that up by saying "that looks like rain to me." That's too bad. You're wrong. It's not raining. That's snow.