I think it really depends on the guy and his face shape and all that jazz. I personally love curly hair. But not many guys have curly hair, so it isn't something I am strictly for. I don't really look at hair all that much, unles he has long hair. Which I hate. But if you can wear it anyway you want, I say curly.
I'd say straight. But not too straight like I mean don't straighten your hair. If it's long then straightening hair is cool but you need to blow dry it straight because that's cool. Curly hair is good if it's extra long but remember to brush it. Curly hair is cool if it's kinda long like Corbin Bleu. It depends on the guy. It's not only the hair. Some hairstyles suit some guys when others suit other guys