My Glock 20C. I have spare barrels for other calibers. One can easily have the parts to make it work with 9mm, .357 Sig, .38Super, .40, 10mm, 9 X 25, .400 Corbon, .40 Super, .45 ACP and .460 Rowland.
10 calibers, one gun. Only the Medusa can rival that. Perhaps a 1911, but it would require more parts.