within the porn world, I'm partial to Sunny Lane's ass and also seem to be finding myself loving Vicky Vette's ass too.
Overall, for me, it's Stacy Keibler hands down. I'd like to wear her ass like a hat.
All great choices listed so far though. There sure are a LOT of nice booty's in the porn!!
edit: oops....I still want to wear Stacy's ass like a hat....but SweetAdri had the finest ass I've ever seen. (I don't consider her to be "in porn" until she does the guy/girl set that she promised to her members 2 months ago. lol!!)