I like her bad. I think it keeps angel foucsed. When he sees darla he knows what he was and doesn't want to be that again.
I did love her when she gave her life. A soul is a huge deal in this show. Humans have one and take it for granted but the undead lose their's get it back and it really hits them hard. If we could always do the right and not have to die and get your soul back first.