Oeilvert: Zidane, Freya, Amarant, Eiko.
Desert Palace: Steiner, Vivi, Dagger, Quina.

I mostly want physical fighters for Oeilvert, but the battles on your way to Oeilvert are quite tough (Armstrong and other enemy monsters) and I level up a lot just outside Oeilvert, so I want Eiko for healing there. As for the Desert Palace, Steiner is the physical fighter there, and I wanted him in the same team with Vivi in case I want to use their magic sword attacks. Vivi uses magic attacks, Dagger heals and summons, and Quina does different things. S/he's also useful in the boss fight for casting spells like Mighty Guard, White Wind and (I think) 1000 Needles.