Vaan- I can't remember what he has equipped atm. It might be a one handed sword. He's typically a fast multihitter (katana types) like balthier

Balthier- Fast Multihitter (cat ear hood and masamune, often berserked and hasted and bravery'd)

fran- "Uses the weapons that no one else bothers with", hand bombs, maces etc.

Basch- Golden Axe dude (has used hammers in the past, if their attack was higher than the current axe available) Tank through and through

Ashe- Save the Queen, paladin, typically has similar armor etc as basch.

Penelo- magic girl with a big stick. Her current big stick is a two handed sword which cracks me up when I watch her swing it around xD Sometimes I berserk+haste her to regain her MP because I've used all of it.

They're all pretty interchangable, barring what their weapons are. I've given basch the heavy irratic damage dealing hammers and axes, ashe has gotten the one handed swords, vaan and balthier have taken the light swords/spears/poles (spears for vaan and poles for balthier) and Penelo had a bow for a long time, and fran gets the novelty weapons xD