I think "Mario + Rabbids Kingdom Battle" is the best game Switch has to offer. No I am not a Zelda fan.
After that I would put Mario Kart at 2nd place.
Odyssey. I'll never play that stupid Rabbid crossover. I don't care if it turns out to be the funnest game ever, just on principle that Rayman deserves better I'll never touch it.
If we are judging based on games that aren't out yet then I say Mario Oddessy. I believe it will have the highest sales of any game on this system and will be the best Mario.