I just finished the game with Zidane (unfortunately), Vivi, Garnet and Freya. It was great fun, but challenging at times without Steiner or Quina.

By the way, you'll want to power up most, if not all, of your characters because at some point, you might be forced into a battle with them. I didn't use Steiner or Quina for ages and was completely owned later on at a particular boss.