I started playing on the Wii U, but now I also have a Switch and Zelda for that. I've made enough progress on the Wii U version that I don't want to start over, but I have enough hours left that it'd be worth it for a better experience. So far they seem identical (besides the controller, obviously). Is there any reason to start my game over on the Switch version?
Content-wise, the games are identical. Switch version does have a more stable framerate (more noticeable in certain later game areas) than WiiU, but if you're not super sensitive to that, it's not a major difference.
The WiiU version runs at 720p@30fps, which is the same as Switch in portable mode, but in docked mode Switch runs at 900p@30fps, which is a perceivable difference on a TV, but nothing extremely major either. The sound quality is also better on Switch with higher quality environmental sound effects.
Whether these differences are major enough for you to start over, is up to you to decide.