Tactics Advance. Mystic Quest I never finished and I never saw what was so fantastic about Tactics. CC I can't play, X-2 I haven't played yet and I don't plan to play DoC anytime soon.

So yeah, Tactics Advance, besides me being biased about it because it was my first FF game, it's an awesome game in its own right and it's shunned or pushed in Tactics' shadow way too much by the FF-fans.