I've played through every FF, save for XI and X-2 (and I don't exactly plan on playing that). The best one that you haven't played is likely IV, but its plot will probably seem somewhat banal to you, for it's been out for nearly 14 years.
I assume you like RPGs a lot, so you could try XenoGears, Xenosaga and/or Xenosaga: Episode II; any of the Dragon Quest games (particularly one from the trilogy spanning games IV through VI), although the crux of each game is within its charm and gameplay; Lunar I and II; and Suikoden I, II, and III.
Since you mentioned FFT, I'd definitely recommend the Fire Emblem series. If you have a GBA emulator, you could download and play any of VI through VIII. A warning to heed, though; prepare to reset and restart chapters often, because unless you want to have your army decimated by the end of the game, you'll want to keep alive as many allied units as possible.