I usually take Edgar cause he would be my lowest level character in this party that isn't Locke or Celes. I then hire Shadow and try to keep him til the end of the Zozo scenario.

After Zozo I usually take Edgar and Cyan or whoever has level issues that isn't Gau.

Oddly enough, I'm probably one of the few people who doesn't use the Figaro Bros. that much. Once Setzer joins I pretty much never bother using Edgar or Sabin and once Shadow becomes a member, I stop using Locke as well.