The parameters you describe are when the gun is used in a fluid, high stress scenario. Under such circumstances, a semi-auto shotgun is less prone to malfunction than a pump, in that the gun's action will not be inadvertently short stoked under the shooter's stress of the moment, with one proviso; the shooter must have enough body mass behind the gun to ensure it fully cycles. Machinery has proven very good at performing simple, repetitive tasks, so relying on an action which reloads itself is astute. But the shooter must be aware that shooting from awkward positions might result in malfunctions if sufficient upper body mass cannot be placed directly behind the gun, particularly those guns with inertia driven actions. It might be prudent to install over-sized bolt handles, for those occasions when the gun must be used like a repeater.
The pump gun will fire each and every time the slide fully cycles, regardless of the position the shooter fires from. But the pump gun performance can be drastically reduced if the shooter suffers an injury to his side, arm, or shoulder, where the semi-auto only has to be manually cycled rearward then released should it fail to eject or bumped forward to fully chamber a subsequent round. So for what is essentially a fighting gun, my preferences in order would be:
1) semi-auto gas gun,
2) semi-auto inertia gun,
3) pump gun,
4) break action, double or single.
With respect to magazine styles, all shotguns have relatively small magazine capacities, so the training related to loading and unloading is critical, and the style of magazine is less important. The shotgun shooter should be able to load without taking his eyes off target, unload the magazine without jacking the rounds through the action, and shell select, where he needs to fire a different type of round than what is loaded in the magazine or chamber. I might lean towards the tube style of magazine, as that is where my comfort level is, and a methodology for continuous loading of the magazine can be worked out, resulting in shorter pauses for reloading.