Ok, by the end of the volume, I can sorta see why some people like Snow. She's kinda went from "annoyingly pathetic" to "adorably pathetic" to me by the end, especially with that end-of-volume illustration (in the full volume, not in the part releases).
Lastiara is still my favorite though. As @Windsagio said, Reaper might actually be the most 'normal' of the group. But, as crazy as Lastiara is, I think she's actually the most mentally stable one, including Kanami. From how she had to step up to take care of Dia after Sieg lost his memories to how she continues to troll the other characters no matter the situation they're in—she's kind of unflappable at this point.
She's stable in the sense that she doesn't change. Her baseline of craziness and love of theatrics remains constant. Or perhaps it sounds better to say she's the most resilient? I kinda get the feeling that if (or rather, given this series, when) something traumatic happens to the team, she'll be the one keeping it together.
We'll see. I'm not reading the part releases, so for all I know I've already been proven wrong in the first 4 parts of Volume 7 that have been released by now.