Mario Odyssey is definitely a more polished game than BOTW.
The reason BOTW wins for me though is that it's the first game in years where I feel like it's opening up new possibilities for gaming as a medium. It's what I dreamed games in the 2010s would be like when I was a kid; that you could interact with almost everything and that from this freedom endless opportunities for emergent gameplay would arise.
Odyssey is an absolutely brilliant game; it takes a proven formula, puts a clever spin on it, and refines it all to a celestial sheen. But the way BOTW weaves a multitude of interlocking elements into an organic and cohesive is for me the greater achievement.