Unless you have a perfect oval face, some short hairstyles will be more flattering on you than others. For example, I have a long face, so I want to create the allusion of width. A chin-length bob or a shag cut that hits at the chin or in that middle place in between the chin and shoulders are great options for me, especially if worn a bit mussy or wavy. The waves add width.
Women with round faces tend to look better with short hair cut an inch or 2 below the chin. You want to elongate your face and keeping hair a bit longer draws the eye downward. Stay away from the classic bob, which can look like a helmet on a round face. A better bet is the long bob, which is longer and therefore more flattering.
Pixie haircuts aren't as flattering on long face shapes. Pixies look best on women with heart-shaped faces or oval faces.