Kirai, hands down. She's got so many options in a given turn it hurts my mind. Optimizing summoning chains. Model positioning. Resource management. Going face tank next to a seishen or full auto with sundering.
Colette will always fuck around with ap manipulation, mobility, and scheme markers. Leveticus will always summon things, kill things, and come back from the dead. Kirai does just about everything. One turn she could be popping out models like Dreamer, the next shell be firing away like Perdita, the one after that she'll zip herself and her pals along like Colette, and the one after that she does a reasonable impersonation of Seamus refusing to die. Playing Kirai gives you so many levers and switches to play around with that it kind of screws with your head and you find yourself pushing and pulling at random and watching the fireworks.