Shotguns for sure, there is probably nothing better than being able to put a hole the size of a plum in someones stomach...oh actually i can think of a number of things that are better. Although, on the merit of wound size I'd say shotgun
Shotguns are effective in close range and they pack a punch but the delay between shots is the only tremendous setback. Reload time is also problematic.
Machine guns require a lot of ammunition to carry around and are not portable.
I would sure as hell go with a trusty machine gun. Sure it's heavy but I have a better chance of surviving.