IX has always been my no.1, but VIII was a close 2nd until I played XII.

I find IX so memorable, I can recall so many moments in the game, and just pick it up and play happily. Where as VIII had a few nice parts but I don't remember a lot of, that said VIII was unique. The battle system was interesting I liked the change from the pretty much the same of the other titles, and the little love story was a nice touch, the ending almost made me cry which was a first for a game.
But like I said IX was more memorable, the music is just awesome, the opening theme is great, the characters were good and a lot of fun to play with.
Also I have played/finished IX start to finish atleast 4 times or more, compared to the once of VIII... and would like to play VIII again but something kinda puts me off it for some reason.
But both are good games, just in different aspects.