So yay, fun fandom times! \o/
I had a hard time with this one because, unlike BtVS, the villains on AtS just don’t do much for me. But after a talk with my muse today – you all know her as damnskippytoo - I realized that my favorite villain have been in front of me the whole time.
There’s nothing more in depth to this than the fact that Darla has the ability to hurt Angel more than any other villain, by virtue of her re-existence. Angel’s history with her is fraught with complicated and deep seated feelings of hatred for the mother-monster who made him - and because she got the chance he would have almost killed for: To be human - and destructive, soul-sucking desire. When she comes back, it totally undoes him to the point where he's running around chasing his own tail trying to, first save her, and then once she's vamped again, kill her.
Because of Darla, Angel pushed his team away, allowed human beings to die at the hands of monsters, and tried very hard to cut off his soul. Just to kill her. She did exactly what W&H wanted her to do – she twisted Angel so far into the game he tried to gnaw his own arm off. She came the closest to making him want to lose the soul. That’s a pretty awesome accomplishment.
Plus, I just like her.