The thing that I liked about Kate was that she seemed more real. Angel has superpowers, he has no family and no ties to the world. Kate and Anne helped ground the show. Angel was fighting for redemption and abstract ideals. Kate and Anne's struggles were more real.
Early AtS seemed like a show that was afraid of committing. There was a constant change in style and focus. I can easily imagine a show where Kate and Anne played a larger part and Gunn did not lose contact with his old gang.
Edit: I seem to have a thing for whiny
character. Whenever I ask someone why they don't like a character I like, the answer is invariably, 'They are whiny!' or 'They are too bratty!' What does that say about me?
Am I just very tolerant or is there something about me that makes me sympathise with these characters?