It's interesting that Darth Maul had a double edge lightsaber, which never seemed to make another appearance in the other films. You'd think they would have been all the rage for the evil ones. Or was it because Darth Maul died with it, that it lost favor in the Empire. Although now that I think about it, Vader probably wouldn't have been as agile as Maul was and that is pretty required for such a lightsaber.