As I recall, classically styled handlebar bars are sized according to frame size. Larger frames had larger handlebar bags, and smaller frames, smaller bags. Berthoud bags work according to this principle, and can be a little harder to fit because of it.

VO style handlebar bags allow for more flexibility. I rather like the rack mounted version, it's stable, easy to use and looks snazzy. If you have the money (which is less than the Berthoud system) I don't think you can go wrong with a Pass Hunter rack and a VO or Ostrich handlebar bag.