The only ones I've heard most, if not all of, are FF IV, VI, VII, and VIII. By far FFVI has the strongest arrangements and includes some of the best songs, not just of that game, but the entire series. Definitely my favourite, not that I'm trying to sell any of the others short. I'd like to own them all at some point. And each of the others I've listened to include songs I'd love to learn to play myself.