That depends on your specialty.

If you are a hardcore user then the best combination for you would be:

Alpha: Bunny
Beta: Ankyo
Omega: Red Battler

If you are a Charm user, then:

Alpha: Princess Noemy
Beta: Jennie
Omega: Juliette

If you are a know-how user, then:

Alpha: Spring Rumiko
Beta: Princess Agate
Omega: Red Battler

Oh, these girls are not very good at fighting, so I recommend you get more.