ashley olsen, vanessa traina (one of the traina sisters), nicole's friend masha, and our own chauss all have the MAXI, which is the largest size.....and the size that i think best shows off the nightingale's uniqueness/rocker-chic-ness. nicole richie has the medium (new leather, gold h/w). i think sienna miller and french vogue's melanie huynh have also been photographed with the medium, but the original leather w/ gunmetal h/w version. afaik that bag comes in two sizes only, maxi or medium.
i personally loooove the maxi!....especially masha's maxi -- a newer thicker distressed leather (diff't from nicole's) with the original thick strap (that has a zipper) + gunmetal h/w + shiny ostrich handles....yum! there are up-close photos of masha's bag in nicole's thread.