I choose Kallen.
She is going to rape your ass when she steals the new Guren. You'll be in Tokyo Settlement raping Black Knights, smug as shit, when you get word shes escaped and think it'll be "fun" to fight the Ace of Elevens.
It won't be fun. She will grab you with her fucking claw and ask you "What is it that is precious to you?" and you'll spit back at her "life!" and then she'll irradiate your punk ass.