Story: FFVI (I want Laguna, Kiros, and Ward to somehow end up in the opera)
Cast: FFVIII (More on the Laguna side of things)
Customization System: FFV (only because I've always heard good things about the job system. I haven't actually played the game yet)
Battle System: FFX-2 (This was just my favorite battle system)
Sidequests: FFIX (Tetra Master! I like Triple Triad better, but I still got some enjoyment from this card game. I really don't spend too much time on sidequests.
Worldmap/Cities: FF XII (No real reason. I thought there were some cool locations... and I'm running out of options)
Music: FFVII (This was tough. I already used the games I would want to put in this spot. I still like the music from VII though)