I like her hair at the end of S4 and loved it when she came back in S5.
I like the short because it frames her face and shows off her best facial features.
The long curly number in S5 was stunning.
The thing about the blond was that it suited her personality. Not that she was a dumb ditz. Blond tend to be more of hard worker at show people that the blond sterio type isn't always true. It showed her girly side.
I liked the long, but it kept her stuck in the rut of her high school days.
The reason her, Joss, David Greenwalt, and the makeup people decided to chop it off was because of the high school rut reason. I have Angel: Case Files S1 and S2 and it had her taking about it. They wanted her character's look to be more grown up and to get away from the old school girl long hair. So they chopped it off.