I know she's old school, but my favorite will always be Jessie St. James. She was a secondary charactor in porn legend Marilyn Chambers "Insatiable" but did starring work in Vista Valley PTA, Talk Dirty to Me and my personal favorite "Her Wicked Ways." She always seemed "real" and that goes a long way compared to the silicone stars of today.
Sasha Grey would be near the top of my favorites because she's hot as hell and she's taken to anal sex like a fish to water but I don't find her sex scenes, and in particular her top-of-her-lungs yelling during sex scenes to be in any way appealing to me.