My opinion probably shifts every time I wake up, but my favorite game (today) is Super Mario RPG: Legend of the Seven Stars for the SNES. I loved all the Mario games up to that point, but had never gotten into RPGs; Mario RPG was my introduction to the genre, and paved the way for me to play Breath of Fire, Lufia, and a host of other RPGs up to stuff like Octopath Traveler, Fallout, and Persona today.