Researchers at the University of Queensland in Australia recently asked 8,520 women their opinion on men with beards. They were asked to rate pictures of men with light stubble, heavy stubble and clean-shaven faces. Women's said the sexiest men were those sporting heavy stubble followed by short stubble. Men with full beards and clean-shaven cheeks were rated the least sexy.
Men with light stubble have the best chance of a one-night hook up with a woman while men with heavier stubble have the best chance for a long-term relationship with a woman.
More on the school where the research was done here