I had four: Final Fantasy 2 (IV), Super Castlevania 4, Super Turrican, and Legend of the Mystical Ninja.
But if I HAD to pick just one, it would've been Castlevania, probably.
Legend of Zelda: A Link to the Past
Secret of Mana
Secret of Evermore
Final Fantasy VI
I still need to beat the first two Breath of Fire games.