When I think of my favourite porn movies, or scenes.... there's no two that really share anything common.
For me, it would have a girl that looks real.... not the 100% perfect stereotypical model type.... someone that you might actually see in real life. Even if they're a bit chubbier or skinny than your average porn star, or with less than "stereotypically perfect" features.... from memory, scenes with those kinda girls have been my favourite.
I don't really like the corny storyline or setting.... like the nurse thing or the air hostess thing or the policewoman thing....
It's all different for me. But usually depends on the girl on camera.