Carli Banks has an immaculate anus. You could eat your dinner off it.
http://girls.twistys.com/galleries/weekly/27/photo/carlibanks/02/images/011.jpg
http://www.solomodelpics.com/carli-banks/celeste-star/11.jpg
Obviously people are likely to suggest their favourite pornstar as having the best asshole. Objectively speaking, I think THIS girl has the prettiest little asshole I've seen in a long time (I believe her name is Jennar Day):
Kaci Starr also has a neat little pucker.