2017 for the Switch, and 2017 for gaming just in general. No year comes close in my eyes.
Breath of the Wild, Splatoon 2, Mario Odyssey on the Switch, just to name a few.
Elsewhere, it was Samus Returns, Hollow Knight, Sonic Mania, Horizon: Zero Dawn, Resident Evil 7, Nier: Automata, Cuphead, I could go on and on. Amazing year for gaming.
Edit: I mean... you could make a shortlist for Game of the Generation with 2017 games only, and it'd almost look legit. It was bonkers.