The Super Mario Galaxy duology has the best overall OST in my opinion. The orchestral music is amazing for so many of the tracks.
For any individual song, however. It would be Weight of the World from Nier Automata. For context:
spoilerit’s the very emotional song that plays during the credits scene of the game, after you complete all 5 of the main endings
EDIT: I want to give an honorable mention to the Ace Attorney OST, across all of their games. A lot of people may know the Pursuit - Cornered theme, but every game in that series has banger tracks. Not as widely praised, and very underrated imo, hence the honorable mention.