I would prefer hair, but if I really liked the guy it wouldn't matter. When you fall in love with someone, certain superficial things don't matter as much. If my boyfriend went bald I absolutely would NOT leave him. That's a silly reason.
I would also like to add that some guys look better with shaved heads. Certain ones can really pull it off.
must have hair. must have hair. long hair, short hair, but hair must be there. and I did almost break up with a guy after he shaved his head, especially because he only did it to win a bet. and I was totally shocked when a guy I had met and talked to online showed up for our first date, bald! and his bare head was pretty unattractive.
now if I was with a guy who lost his hair, that wouldn't bother me. but purposely getting rid of a head of hair? I'm so sad :(