This is pure opinion on how useful or how they are used but see the following
Offensive Flying Myths:
Griffens
Ladons
Manticore
Harpies
Offensive Ground Myth:
Erinys
Offensive/Hybrid Ground Myth (Very Situational):
Minotaur
Cyclops
Medusa
Saytr
Spartoi
Defensive Flying Myth (Situational):
Pegasus
Defensive Ground Myth (Very Situational):
Centaur
Cerberus
Caledonian Boar
Naval Myth:
Siren
Hydra