Mostly everything, but those that I really enjoy are the ones where the girls seem to enjoy themselves. Expressions and sounds, yes, but also other signs of arousal - heavy breathing, hard nipples, flushing in the chest and ears, involuntary little twitches/quivers, etc.
To be honest, it has to look real. If the maoning sound like she will take off to the moon, well thats one huge turnoff.
Also i dont like to see the guys ass. i prefer to see the penetration and cumshot.
All of it tbh. Not a big fan of the camera angle between the dude's legs where all you get is a hairy ballsack swinging back and forth in front of the camera.
Ass, tits, face. Usually in that order. Fucking love looking at a girls asshole, and watching it get penetrated slowly. Yet, I hate nothing more than slow-mo in porn.
I seem to primarily focus on the situation and the girl, her clothes, face, hair and so on. I like to imagine what she's thinking in the moment, like does she even seem to like the guy penetrating her, is se doing it for money and so on. looking for flaws in their way of acting where their own personality breaks through xD