There are downsides to this very simple voting system. Someone like Calypso could be the second favorite of a lot of people and yet end up in the bottom of first favorites. The ideal system would be everyone putting a 1-5 rating to every girl, and then arranging them after average rating, but that would be manipulated as some people give 1's on the girls they feel are too highly rated (as we see with the game reviews on this site, IMDB ratings etc.). The best system in practice is probably to select your top 3 (or top 5) and give these 3, 2, 1 points respectively and then look at the sums.
With that said, generally I dislike these votes as they just lead to animosity and they overshadow the fact that Caribdis has managed to create a cast of LI's that are all universally beloved. I'm confident that every girl has at least an 80% approval rating among the fans, yet the votes make it seem like people don't care for Calypso, Nancy etc.