Beretta or SIG 9MM.
These are the weapons our military uses. Ammo, magazines, and spare parts will be available regardless of what happens.
And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.