Odyssey and it ain't even close.
Wonder will hopefully be awesome and drag 2D Mario out of the staleness and mediocrity it got into over time with the 'New' series. Then again, I'm not sure it won't just be a prettier, wackier version of the 'New' series, which would be unfortunate. Find out in four months. Best case scenario it makes 2D Mario awesome again. I'm going into the game with cautious hope that it doesn't just look different from the 'New' series but will play totally different as well.
But Odyssey!... Odyssey was one of the absolute top reasons to get a Switch in those first couple years. Odyssey is a premier title of the entire generation, all systems included. Odyssey was like Mario 64 twenty years later. Odyssey is in the discussion for best Mario game ever. And it was a HUGE game for being a platformer, most even 3D platformers are like half the length or less of Odyssey. Hell, I 100%'d all of 3D World except the final post-game world, and 100%'d Bowser's Fury, in just over half the time I spent on Odyssey probably only having like 80-85%'d that game. Odyssey is one of those generational titles from Nintendo, and, to the point of the question, asking about how excited we were when it was revealed, Odyssey looked like it was gonna be the sort of generational game that it turned out to be. Mario Wonder looks like a potentially cool wacky new 2D Mario, but I don't YET see anything suggesting its gonna break new ground or be one of the absolute best games of the generation.