Well, I like Zidane/Dagger/Amarant or Freya/Vivi or Eiko. Because Eidolons rock.

No, seriously. If you do Chocobo's Hot and Cold, you get enough jewels to make every Eidolon very good. And you get a LOT of Ore, that you can use to pump up summons even more, or you can pump up Leviathan. You don't know of how useful a pumped Atomos is against Grand Dragons. XD