I suppose it depends on the medium, but in most cases I like physical transformations better.
In books you really have to rely on the mental changes to see how a character progresses but in mediums like cartoons, anime, manga, and movies, the character can actually evolve and become grander than they were before with a physical transformation which usually accompanies a mental transformation as well.
Romans 8:31 What, then, shall we say in response to this? If God is for us, who can be against us?
1 Corinthians 13:1-3 If I speak in the tongues of men or of angels, but do not have love, I am only a resounding gong or a clanging cymbal. If I have the gift of prophecy and can fathom all mysteries and all knowledge, and if I have a faith that can move mountains, but do not have love, I am nothing. If I give all I possess to the poor and give over my body to hardship that I may boast, but do not have love, I gain nothing.