All of them... Even if I voted for medium length. Short one is little tricky. If it's done properly to suit your face cut, hair texture etc. it just looks magnificent! Also the way a woman carries it off also matters a lot. Longer one looks beautiful and feminine if they are well maintained. It's a little hard though. Tried doing it once and failed miserably. I got split and thinner ends+ frizz which looked really weird. A good male friend of mine once politely said that they look ugly. Then I came back to medium length. Medium length is safe thing. You can hardly go wrong there. It's easier to maintain, always looks good.
I prefer short-medium hair length on women because I feel like it shows more of her beauty. It's just way harder to pull it off nicely. Long hair is kinda boring and looks the same on everybody really..
It depends on the individual face and features of the girl. For example, a lot of girls may be able to pull of the short haired look, but most would indefinitely look even better with long or medium hair. There is the occasional exception where a shorter hairstyle looks better, as it highlights the facial structure and features. However, for most girls, I'd say longer hair (shoulder length or longer) looks better.