Aayala secura

I'll politely disagree with your first sentence ;)

I've got a fairly full group of maxed out toons, so who would you use in her place? I'm always up for trying something new. Needs to have good enough HP to survive the initial Wedge, Biggs, and Lando shots. I want a fairly reliable stun, and at least medium damage

That's fine if you disagree, we have different play-styles and strategies. One of my main squads focuses on TM manipulation to keep the other squad's TM down as much as possible, and Aayla doesn't have a place. I've done the "big-character" thing with counter attacks (Jka, Aayls, 5's, RG, SF) and it wasn't bad but I still landed around rank 15 every night. It really just depends on what you're trying to do with your squad. Personally I've just found that I can almost always find somebody that better fits into that spot, just my opinion.