And not a single person challenged my choice of ONLY one gun or even ONLY one band. 
Only one gun? Well I would want something that the government has banned. If they banned it, it must be super effective!
73 John AF5CC
I am sticking with the 12 gauge, because of the versatility. Remember your "one gun" must be able to feed yourself if necessary, and small game to large game can be taken with the 12 gauge by having the proper loads as well as defend yourself if necessary, again by proper load selection. And the pump action is the most versatile because of the ability to cycle the very lightest loads up to the most heavy hard kicking slug load without worrying about whether the action will cycle this wide range of loads and recoil impulses.
Some of the same could be said about a center fire revolver (say a .44 Magnum) because they can function with very light custom loads suitable for taking of small game all the way up to heavy loads suitable for defending yourself from the largest predators on the North American continent.
But I still say most people would do better with a 12 gauge pumpgun. Again this is all hypothetical, as here in America we don't have to get along with "only one gun". NOR do we have to get along with only ONE band for digital modes. I operate all bands for digital modes 160 thru 6 meters. You should too.