Valkyrie: Rider/Saber

Achilles: Saber/Berserker/Lancer

Dragon: Caster/Assassin/Rider

Hyperion: Lancer/Ruler/Caster

Helios: Saber/Avenger/Rider

Belial: Caster/Assassin/Berserker

Just a random thought in my head. You can change their classes if you want.