The male nude is difficult to photograph in an artistic fashion as it is too easy to step over the line into just another cock picture. Some of my best male nudes emphasize the masculine component of the subject. The solid muscular build and postures of strength yet gentleness. The penis is just part of what it is to be a male, but due to its rather exposed position it can dominate any nude photo. Therefore glimpses of what is there seems to work best for me as well as in a flaccid state. Although, if done right, an erect penis is a powerful statement as well. The image works best if it tickles the fancy of the viewer leaving some room for imagination.
The female nude is an absolute joy as just about any creative photograph is beautiful due to the nature of the subject material (of course some are more than others.) How can you go wrong with the soft curvy outlines of the feminine body. Just as a picture of a lovely flower. I would love to help any aspiring model fill her portfolio with lovely nude artistic photos. What does make the female nude difficult is making it stand out from the billions of artistic photographs that are out there today. It is important to me to find out what is unique in the particular model to be imaged, and the work around that uniqueness to create a one-of-a-kind image to be enjoyed and admired by all.
Well, enough of my amateurish photographer ramblings - there are probably some professionals reading this that are rolling their eyes - to each his own, but the results do tell the tale.