When it comes to mages what you want to look for is attack.

So Atk Increase Skill > Splash Increase Skill > Other Skills

Of your choices without being gender bias. I'd just Mehlis, Pallis, and Barbie.... or... Mehlis, Cyrus, and Barbie after awakening.

Though as mentioned before you would hardly need three mages late alone mages at all later one. Bishops seems to out perform them for the most part, and if you have Solano... well ya. Garania is probably the only mage we have that can out perform Bishops. Odette is simply for Magic Reduction. Sasha is simply for physical reduction (by allowing dodge). Really wish we could get Moldevort with her Atk increase skill.

Though this statement is likely to change once mages finally get their AW skills.