On my first playthjrough, I took Zidane, Steiner, Amarant and Eiko. Then I realised that Eiko can't heal me in there and wasted a damn trance when fighting Ark, I changed on later ones.

Now, I always bring Zidane, Amarant, Freya and Quina. I leave Steiner with Vivi so he can use the uber powerful maigc swort combo.