I have not once voted (maybe I will next time), but I think that I would take into consideration things like:
1. Longevity of career
This should favor Irina, Michelle Kwan, Mao
2. Whether or not all the jumps were there with no wrong edge or rotation issues
This criteria should actually have favored Miki, if anything. Miki should really get more recognition for being the jumper that she is.
This in my eyes should favor Mao absolutely and least favorably, Irina. I have never found her particularly enjoyable as a performer.
4. Ability to do big tricks such as 3-3 and triple-axels
This should favor Yuna as well as Mao.
5. Off-ice behavior
I think Michelle Kwan has been quite impeccable in that regard. I, being a fan of Mao, find her off-ice behavior inspiring.