FFIX, because obviously I would pick FFIX.
FFXII, because it's a thoroughly enjoyable game in every sense (I even enjoyed grinding!) and Balthier.
FFXI would be a great addition, because if I'm on a desert island - with a PS2 and internet connection - then it would be a cool way to pass the time. I played it for the trial period, but I didn't fancy the subscription cost, otherwise it's definitely a game I'd've liked to sink my teeth into a little more.