I think anyone that gets offended if someone finds a particularly pornstar they like ugly or unattractive is both hilarious and silly.
Having said that, I don't generally like the majority of porn girls in porn so listing all of them would be tiring. It will just be easier to list what I generally find unattractive: too thin, too much plastic surgery; including fake tits, botox, etc., too much cellulite, no curves in the right places (flat chested or pancake ass), too much fucking make up, and generally a face that I find unattractive which is really just a matter of personal taste.
Granted there aren't too many women that can fit all this criteria so I tend to let one or two things slide depending on how bad each particular case is. But I generally decide to keep a porn scene depending on the chemistry of the performance rather than the look of the woman. I have a few scenes of woman that aren't as attractive as those that are more popular or more attractive due solely to how good she performs at her sex (Holly Michaels is a perfect example of that).