No character is completely useless, even if you had a party made up entriley of the suckiest characters, you could still beat the game. So it doesn't really matter.
Personally I choose to use all my characters and balance them out. I always choose whoever is the lowest level to be in my party, and when they're level gets higher I switch them out for the new lowest leveled character, rinse and repeat until the end of the game where I use whoever the hell I feel like for the final boss.