I love Larxene; she's such a fun villain and definitely one of my favorite Organization members! Her battles aren't too difficult for me, except that they mean I can't use my favorite spell, Thunder, because it just strengthens her. That always crippled me a bit.
As far as her attitude goes, it seems like she treats everybody in the same, haughty way, but with some "finer nuances," as she would say. She pretty much considers herself the Queen of All Things Awesome, but I thought she showed some respect towards Marluxia, since he was the leader of their little scheme, Axel, albeit in a very flirtatious way that quickly stopped after she realized he was a traitor, and Roxas...once he'd proven to be somewhat competent, that is. She only gave him a Potion after she'd heard he'd improved. Obviously she likes to kick Sora, Repliku, and Vexen around like a couple of footballs.
Favorite quote? Ummmm...from the game, it would probably be, "It'll kill you to hear this, but I think I can live with that!" because it just sums up her attitude so well, and it's pure evil but in a kind-of hilarious way. Also, from the novels, her entire conversation with Axel when they first met properly. It was just so funny, between her asking him random questions and him thinking, "...what?"