I voted for Aslan because He was placed on the ballot; but it hardly seems fair to make others compete with Him. It's like saying, "Whom do you like better, your neighbor's friend's nephew, or the Almighty God Who created the universe and gave life to all creatures?"
Of original-to-the book characters who are not Deity, I also strongly favor Peter. There is so much male-bashing in Western society--at the very time when we frankly need MEN to do the bulk of the fighting against global terror and tyranny. The plotline of Peter ascending to heroic young manhood is a valuable illustration of unabashed male valor and virtue, made available at a time when we sorely need it.
I enjoyed Oreius, too. He was like the smart veteran sergeant in old war movies: heroic in his own right, AND helping the star of the movie to look good. Also, his solemn presence when the Pevensies first entered Aslan's camp was a good buildup to their meeting Aslan Himself.