I adore Edmund. He completely turns around and regrets the mistakes he has made and the people he has hurt. Everyone makes mistakes and Edmund to me seems one of the more believable characters in the book.
My least favorite character was the White Witch, even though she was pretty cool...literally.
*Spoiler*
I was also really sad about what happened to Susan in the LB. She was one of my favorite characters. I think that there was still hope for her though. At the end of the LB she was still young and had just lost her entire family. I think that in the end she will once again become a "friend of Narnia." It also says repeatedly in the books "Once a King or Queen of Narnia, always a King or Queen of Narnia."