Okay. First, I'm a tit guy who loves naturals and I don't watch fake tit porn so that limits my exposure to only a few American girls that I follow.
My favorites at the moment from America are:
Gianna Michaels and Aurora Joile.
Among busty natural babes (non-BBWs), American porn stars are not as hardcore as their fake breasted/small chested counterparts. I used to be a follower of Brandy Talore and Sara Stone, both of them very gorgeous, yet they were mostly great for looks and not so much for performance. Both really disappointed me for not doing anal scenes.
Gianna Michaels is really hot with the perfect set of tits and ass and her performances and attitude on camera really turns me on. She fucks like crazy, swallows many loads and has even gone so far to do bukkake. My only complaint for her is that she has only done anal once (Big Wet Asses 15 is my favorite scene of hers, she has such a sexy ass).
From Europe, my favorites at the moment are Jasmine Black and Sensual Jane.
Where American porn is really great with attitude, European porn is very natural. You don't have the aggressive yelling so much and the dirty talk but see more love making. The women are much hotter overall, especially the Eastern Europeans with their big natural tits. Best of all, I get to see model beauties go at it in hardcore sex having anal sex and double penetration like it was no big deal.
Overall, the average European is better than the average American porn star. There are exceptions like Gianna Michaels who stand above the world.