IGN posted some comparisons, I guess the Switch version does look better and more colorful.

and another one from LipeJJ's link

Ya it is very noticeable I wonder however if the final Wii U version is truthfully not more polished.

Well the Wii U version will have to do.

Yea the Switch version looks better, specially when Link goes on that cliff. You can see way more trees and etc in the distance.

colors, draw distance, shadows, resolution and less aliasing. I'm cool with this.

This version is good to notice the differences: https://youtu.be/_ZuxgLcgpFk

Notice how much more details appear when he's on the cliff. Gee... no to mention it seems much more stable (with less aliasing and everything).

The difference is about CAD 452 and calibrating your tv correctly. Apart from a few extra details it looks like the difference between limited and full RGB all over again. I'm sure it will be picked apart on release to see if it's worth and extra $300...
Where's the comparison between docked and undocked mode.

I like the sky in the Wii U version better. Looks more natural to a normal sky. Otherwise, not much difference. Is there a different shader being used between them?

Edit because just watched the vid that got edited into the Op after my posting. That one shows Switch version being way nicer.

You also have to remember that for whatever God forsaken reason, Nintendo decided to make the Wii U not display full range over HDMI so unless there are future home brews allowing that, you are going to miss some contrast no matter what. As much as I love my Wii U games, technically, it really is a shit console with a lot of shortcomings. 

im not getting a switch for maybe 4 years lol so i gotta stick with my wii U. i think the wii u version looks decent.