Most Helpful Guy
I like long hair on girls. For me, shoulder length is kind of a minimum, and it's hard to imagine "too long" until you're in Crystal Gale territory (her's dragged the ground).
For girls with straight, or fairly straight hair, "small of the back" length is just awesome. It's harder to go that length with curlier hair, but at least shoulder length for me.
IMO, very, very few girls can pull off the short haircut well. Most make you look either old (all women go short once they hit 50 or so, and give up) or butch. The very few exceptions that I've ever found attractive tended to be Euro cuts, but you kind of have to be a Euro girl to pull it off.