Edmund is my favorite Pevensie. I like the others, but there's something about Edmund that makes me like him best.
When The Lion, the Witch, and the Wardrobe begins, Edmund is a jerk and a bully, particularly towards Lucy. When she finds Narnia, he has to torment her about it, and when he discovers it is real, he is worse, lying about the fact that he had been there too. Yet he gets worse. Once all the Pevensies are in Narnia, he goes to the White Witch and tells her where his siblings are, betraying them to the very person who wants to kill them.
Why, you may ask, is this Edmund one of my favorite characters? Because the story doesn't end there. As Edmund travels with the Witch, he begins to see her for who she really is, and repents of his traitorous deeds. He wants to get back to his family, but being rescued and brought to Aslan's camp still isn't enough. Aslan had a talk with Edmund which no one else heard, which truly changed him. But to complete it all, because of Edmund's treachery, the Deep Magic from the dawn of time required blood as atonement. Aslan sacrificed himself for Edmund, and came back to life due to the Deeper Magic from before the dawn of time. Edmund was truly changed after this whole experience, so much so that when he was a king of Narnia, after he helped to stop Rabadash's attack at Anvard and they were discussing what to do with him, he said, "But even a traitor may mend. I have known one that did." Even though Rabadash's grand scheme was to kidnap his sister, Susan, and force her to become his wife, Edmund was still willing to show him mercy, for the mercy showed him by Aslan.
Edmund obviously felt bad for the way he treated Lucy. In Prince Caspian, when the children disputed whether to go where Lucy had seen Aslan, or follow their own path, Edmund sided with Lucy. He even says it is because of what had happened the last time, and that Lucy had been right then. Later, he's the second one of the party to see Aslan, before Peter, even.
The movies leave much to be desired, but one thing they get right is Edmund. (Prince Caspian gets Peter all wrong, and it's aggravating, but he's not the subject of this post.) He is a repentant traitor, who mends his relationship with his sister so well that they become very close. Indeed, the relationship between Anne and Edmund Rubin was influenced by Edmund and Lucy. He isn't perfect, he sometimes gets cranky and he isn't as patient as Lucy, but once his positive character arc is complete, he doesn't reset. He never goes back to being a traitor. He isn't free from temptation, Deathwater Island shows that, but he can overcome it.
I think I like Edmund because he's easy to identify with. I never was a traitor, but I was a brat. People who have only known me as a teenager have a hard time believing that, but it's true. I was bad, and I did have to reform. I'm not perfect now, but I'm working at it. Edmund shows that a traitor may indeed mend, with Aslan's help, and that's something we all can benefit from.