I don't really have a preference myself but I think that sometimes, people tend to be attracted to what is similar to them. For instance, my boyfriend is a tall, blond-haired guy with light blue-green eyes. I am quite tall with blond hair and blue eyes. We have the exact same shade of blond hair too, which is quite uncommon. The ressemblance is striking enough that we've been told by a couple people that we look alike. Someone even asked us once if we were related!
I couldn't care less about his hair color unless it's something like White or Gray or some unnatural color. But if I had to pick I would say dark hair I don't really like blondes that much in general I think it makes some guys look really feminine.