I've loved Willow from the beginning.
She's adorable, she's sweet, she's funny and intelligent. She has grown immensely over the course of the series. She's human, so even if I don't like the magic-addicted, manipulating, flaying-people-alive Willow (and really, who does?), I can understand it. She has insecurities - a lot of them - but she's a strong character that's always changing and fighting. She's a pillar for a lot of the other characters (Buffy, Xander, Tara) but at the same time you just want to hug her and support her right back.