It depends on how the girls looks, dresses, and how she does it.
I saw one of my favorite porn stars, Luna Lane, masturbate in the back of a limo, and then on a couch. The problems for me were, in the limo, she wore shelf-toe Adidas. I love Nike Shox on girls, and it was Luna Lane that made me love shelf-toe Adidas on girls too. But she never took them off. She wore black suede heels in the sofa masturbation scene. I need a girl to be totally nude when she is masturbating. I saw a super tall redhead stunner named Winter Lane, and she masturbated on the bed in stockings and in mules. I am totally against shoes in bed during sex scenes.
But getting back to my first point, presentation is the most important thing for me.