So, attractive means a different thing to every single one of us. That said I will speak on my own tastes, which are admittedly kinda broad. I have found both more and less attractive anuses, much like similarly describable vulvae, are fairly equally distributed among women of just about every shape and size. Proportionality is in no way consistent, neither is appearance. Most are beautiful in their own way and I have been thankful for nearly every one of either that I have been granted access to. Some are definitely "better" than others, though I am certain that this is more a matter of preference than anything quantifiable.