Of the ones I've played, I have to say FFIV. For years I never really gave it a chance, but then I picked up the DS version and it only confirmed my dislike for it. There is nothing wrong with the story, or the characters, really, but the difficult level just destroys it for me. The elation you feel after you've beaten a difficult boss is short-lived, as the next one is three times as hard. It is extremely unbalanced, and it just ruins the game.