1. Final Fantasy Tactics 2. Final Fantasy 7 3. Shadow Hearts series (kinda need all to appreciate, due to story connection)
Would love to say Xenogears, but Shadow Hearts Covenants and it's final 2 hours or so made the game so complete, while Xenogears is incomplete game. I have to lean towards shadow hearts for that alone.
Speaking of which, **** you Square for not completing Xenogears.