my 2 cents (i'm level 54):
1) Ariel - nice dmg dealer, for now my favourite, but i'd like to see her in the future, in harder situation.
2) Gale - cool support for all team (expecially physical one), with silence and increased attack.
3) Flora - a must for some spot, cuz it's the only healer in this game.
4) Mariana - great for crusade, with her ultimate and her 3rd skill (AOE dmg)
5) Alana - need to test her more, but good in some situations.
6) Esabel - unique female tank, but not a real tank...useless for now.
7) Selene - nice single dmg dealer.
8) Arachna - need to test her more
Need to get others female hero, but i think this game lacks on a real female tank (maybe a barbarian style one, cuz there's an amazon, Leah, yet).