Sexiness is not
equal to bust size at least in my opinion.
For example:Is disgusting, and it is by no means the biggest offender.
My favorites would be:Chun-LiFilia
Followed by Deedlit (Lodoss) , Priss (BGC), Eclair (Kiddy Grade), and others would be tops of my list. I would add Ranma-Chan but she's technically not a woman, and I would also add Brianna and Julia from Gold Digger, Barbara Gordon from DC, and She-hulk from Marvel, but they're not anime characters.
Note that while I find those I listed 'attractive' I do not like hentai in the least, nor do I have some great fantasy about any of them.