I think this was a good idea for a thread, it is focused on one (perhaps the most crucial) aspect of composing. It would be interesting to have an entire sequence of such challenges, best harmonic progression, best orchestration, and so forth.
Here is a link to the B theme, the Princess Anna theme, of my piece Saint Vladimir. The theme sort of gradually morphs through several iterations. When the trombone sings with the woodwinds, the trombone represents the voice of Vladimir.
I think this is my best melody so far, but perhaps I will write a better melody tomorrow.