I voted Lucy, because she is closest to the main character in LWW, PC, and VotDT. She's the one that discovered Narnia, and she seems like the most faithful to Aslan. I like him just as much as I do Lucy.
My 7 year-old great-niece Cammy says that Aslan is her favorite character because he is a Lion. She reports that she has read 4 of the Narnia Chronicle books with her papa, my nephew Bryan.
My favorite also is Aslan. He is mighty and powerful yet merciful and loving.
I think Lucy has a closer relationship with Aslan (not that I'm prejudice or anything, but she really does see Aslan more often than anybody else in the books). And Edmund really believes Aslan and Narnia after he's been forgived, which makes him a great king.
I think either Aslan or Lucy is my favourite character. Aslan because he is very powerful and omnipotent and omniscient. Lucy because she has the capacity to believe the impossible, which is something that is not encouraged in society for whatever reasons.