Hair on the shoulders (#1) should be avoided at all costs. All of the other hair positions have their place depending on your model and the look you are trying to achieve. The reason I shot the hair on both sides (#4 and #5) is because the natural part in a person's hair will lend to one side looking better than the other.
Generally you want their part facing the camera so more of their face is included. For this tutorial, I chose hair up (#6) so we can more easily see the posing instructions without distraction. Many women see ponytails as the "day-off" hair style, but it actually lends itself very nicely in portraits and headshots since you have clean view of their face.