In winter I think it's bad to be nocturnal, you need Vitamin D exposure. In other seasons, you'll get enough incidental Vitamin D exposure, so as long as being nocturnal doesn't reduce your mood.
I believe it is most productive to work to your body clock preferences, whether you are an early bird or night owl. Societal arrangements generally favour early birds, so some of us are just permanent double shot caffeine addicts in the A.M.