Mia or Karla?

IMO, I would choose Karla over Mia. Karla is a bit more offensive than Mia. Karla with the Fury, Wrath, and Even Speed Wave can boost her damage to the maximum with her blade. Their BST is just 1 point different so it won't make a big difference who you choose. But it's your choice at the end.

They're both a ton of fun, so it doesn't really matter who you use. On that team, they're pretty much the same, but I think Karla would be just sliiiiiiiiightly better in terms of consistent damage output... Don't sweat it, use either of them haha~