For the last couple of years I have been slowly reorganizing by gun collection with the basic idea of "Two equals one and one equals none." I have been trying to restructure so I have a lot of similar guns, guns that share parts, magazines or accessories. The idea being that if one gun became damaged beyond repair it could still be used as parts for the others. Also the accessories like holsters, mags and the ammunition could still be utilized for other guns that I own.
The question supposes that you are in a situation where you could no longer acquire any more guns, parts or ammunition (or even reloading components) from what we Americans would consider "normal" venues (Gun shops - Gun shows - Mail order etc.). Whatever you might obtain would have to be under the table, there wouldn't be much of a selection available and it would definitely be potluck.
So here's the question - Would you prefer a selection of guns in common calibers that shared ammo and parts? Or would you want a wide variety of weapons in as many calibers as possible so that you could take advantage of anything that might come your way?