Taking into account only exclusives (which I think its what this thread is intending given the poll) its gotta be Mario Kart 8 Deluxe.
Yes, perhaps its mostly a WiiU game, but its still the best for me. The best in the series and the best Mario spinoff ever, incluiding all Mario Parties, Smash Bros, Yoshis and Luigis Mansions. I cant put into words how much enjoyment I've had with that game. So yeah, its the best. For me, that is.
Following it:
Breath of the Wild
Astral Chain
Xenoblade Chronicles 2
Link's awakening remake
I suppose Fire Emblem 3 houses would be my 6th, but theres a significant margin between them. I still have plenty of issues with it.