First off, there's no "best" because of the variability with how you build your characters. That being said, I'll address this in one of two scenarios.
If you want masters who play to your character's strengths: Ryu: Bunyan, D'Lonzo, or maybe something more neutral like Bais Nina: Emitai Rei: D'Lonzo Garr: Hachio Momo: Deis Peco: Fahl
If you want my opinion: Ryu: Giotto for quite some time (AP and HP help his dragon forms immensely), then switch over to someone like Hachio Nina: Emitai Rei: Meryleep, then Bunyan when you're happy with his agility Garr: Bunyan Momo: Either Bunyan (offensive ideal), Emitai (healing ideal), or Deis for an awkward in-between Peco: Giotto until AP's in the hundreds, then Fahl
Right now I have Ken (AKA Ryu :) ) with Bunyan, Garr with Fahl, Momo with D'Lonzo, and Nina with Mygas, and I'll put Rei with Meryleep when I get the chance. --- Currently playing:Breath of Fire III/Solatorobo