Attractive, that is very important, I want all the actors and actresses to be attractive. People I would want to be with. Then a variety is nice. Some people just nailing the hell out of each other, others going a little slower. A variety of positions. And I like more for-play. Going right into oral that leads straight to sex is disappointing.
More then anything I want to see people enjoying what they are doing. There are some times and characters when either one going through the motions is nice, but generally people enjoying the sex.