Final Fantasy VI and Chrono Trigger/Cross are the objectively best game soundtracks of all time. Honourable mentions to (in no particular order) the entire Zelda series, FFIX, several entries in the Dragon Quest series, several entries in the Suikoden series, Secret of Mana, Seiken Densetsu 3, Super Metroid, a bunch of Motoi Sakuraba soundtracks, and a bunch of other Yasunori Mitsuda soundtracks. There's probably more I'm not thinking of but that's a fair kickoff selection.