Shotgun, without a doubt.
Video games tend to portray shotgun as being a point blank range weapon, but that's just for balance. Shotguns have a suprising amount of range, shooting clubs used to use/still use shotguns for plate shooting (<-- involves launching a plate tens of meters into the air in a horizontal path overhead/in front of the shooters), to put it into perspective.
Shotguns pack massive punch, actually have decent range, and wouldn't be as dangerous or heavy as rocket launchers, LMGs or anything inbetween. If I'm out in the wasteland, I want to run away from whatever I can run away from, and use my gun in emergences, because the bad guys can get fairly close to me without me being able to escape, making the shotgun a perfect weapon to use.