To me honestly it depends on what the guy looks like.guys can look so-so depending on how they pull it off. But in my opinion I'd perfer a guy with shorter hair usually when I see guys cut off their hair they look 100 percent better/cuter.
My ex had shoulder length hair and he cut it reccently like a couple years back and he looks WAY better. Me and him are still friends lol but yeah cutting your hair does improve your looks because it's cleaner, more manlier and I don't know and it doesn't hide from your face.
If your hair is healthy and not dirty/greasy or dry then I think it can look pretty hot on some guys. If you have the face and confidence to pull it off then go for it. However, if it goes far past your shoulders then you risk looking like a manly chick :P. Personally, I think it looks best when it's straight and a darker color. Like on some native guys! If its curly though, I usually find it to be a turn off.
As long as you can work it, short and long are both nice.
i like this link that's basically shoulder length but when it's longer than that,it could go either way,sometimes it's hot (if the guy is right,the hair is right) but sometimes,it looks too...''nurtured'' and I'm not really into it linklink but still,it's just hair,not a big deal