I try to train everyone up but it's obvious I play favorites. I have three set ups basically.

My main party is Basch(Tank/ Samurai) Lady Ashe (Mage Knight) and Balthier (Jack of All Trades) I usually use Balthier in this set up and basically help whoever seems to be lacking as the battles drag out.

My second party is Fran (Archer/Lancer) Vaan (Mage/Thief) and Penelo(Sage) Their designed for speed and magic and they're my secondary party.

My third set up is Balthier (Gunner), Fran (Archer), and Penelo (Archer/Mage) I only use this set up when dealing with obnoxious flying enemies.