I just use Vaan, Basch, and Ashe. It's very tough for me to change after working on a character. I only switched from Fran to Ashe because of her superb magic stats to start out. I really like Balthier's character, but I also really like having a well-rounded, specialized party (Basch - fighter, Vaan - all-around, Ashe - magic). And it just wouldn't seem right not to have Vaan in the party.