Well my usual party is this:
Zidane: Because I have to apart from in Memoria
Garnet: Summoning and Healing
Steiner:Climhazzard!!!! Minus strike is also good if he only has like a few HP left.
Freya: Jump!!!! Also for Dragon's crest and Reis's wind to help Garnet with the healing.

In Memoria I use Vivi instead of Zidane.