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.