'Moe' is used to describe any traits that are deemed desirable by otaku. As such whatever is popular can technically be considered 'moe'.
Now I'm simplifying it a litte bit and the character who wins is not necessarily a perfect personification of what is currently considered moe but still, the character who wins wins because people took a liking to her for one reason or another.
If one wanted to determine which traits are really seen as most desireable (and thus moe) you'd have to use exactly that instead of the characters, i.e. run the tournament with 'blonde hair', 'brown eyes', 'nekomimi' etc. as 'participants'.