The overall cosmetic appearance is the most important thing for a penis. This was the result of a survey done some years ago with some women after the scientists asked them to rate the most important features of penis. I can look for it if anyone is interested.
The results are quite obvious. I think a penis can be aesthetically beautiful or, even better, they can be not ugly. It is just like a cute pussy: it can have a powerful visual effect. A proportional head to the size os the penis, a symmetrical penis, a penis that is not curved to the right or left, the color of the skin, the body hair, a little bit of girth.... Length was one of the least important characteristics.
I guess that if I were a woman and I had to suck a penis, a nice hygiene with a "good looking" penis would make my job easier, but I already saw so many weird looking penises around here that I have nothing but deep respect for the women that are willing to BJ them.