Depends on the distance---------------
If your fighting in a jungle with very thick, and dense undergrowth, or inside of a residential home, or "close-in" area, where ALL or 90% of the targets are going to be within 40-50 yards, I'd use the 12 gauge-12 pellet magnum OOBUCKSHOT load made by Winchester, in my Winchester Model 1300 Defender.
Why, leagallity, able to get one easier, it works fine within the distances metioned above, got more experience with the shotgun, the need to aim as precisely is NOT QUITE AS CRITICAL, and it has more knock-down ability at close ranges from what I'm told (I've never shot anybody myself) but I've seen a person get shot with the above mentioned BUCKSHOT MAGNUM load, and I would not use any otherload-it was a one-shot-stop, took the fight right out of the suspect instantly, he would have been unable to fight back no matter what he had in his hands(hit in the throat at 10 feet away). And also a person of the older generation is going to have plenty of respect for the shotgun, a person of the younger generation has been brought up on a steady diet of seeing submachineguns ripping across the computer screen.
Of course, if he had taken multiple hits with an H&K MP5, or UZI, it would have probably had the same results.
Precise aiming is needed with both, unless your just sweeping an area to catch whom ever it my be in the way, such as in war time house clearing.
The shotgun really excells at nighttime, even with nightvision scopes, according to the World War One Doughboys of the AEF, that is the shotguns forte( I agree), I've searched for burglars in many a building where I'd rather have the shotgun in hand instead of ANYTHIING else.
A when the shotgun was presented, ALL-- as in 100% of them gave up right away.