II and IX.
I honestly am not sure why I like II so much. I think it's that it's fun to play, and I like the story. I mean, it's not on a par with the latter FFs, but that's only to be expected. I also love the music. (And the disturbingly pretty arrogant bastard of a main villain, but that's just me.)
IX is an all-around great game. Excellent story, music, characters. Characters with believable motives, at that. Also, it has the most addictive mini-game in FF history.