As the former lead instructor for my agency, which issued the AUG, let me add my bit. One problem with the AUG (other than cost), is the high sight line above the bore. At very close ranges, given your hostage rescue scenario, this is a problem. Also, the 'rear' ejection can be a problem if you are, say, right handed, but the only cover is to your right. Both of these issues can be overcome with training.
While I own a AUG and a shotgun, I would go to a handgun for interior defense. I live a long way (2 miles) off the road, so a rifle is fine for exterior defense in my case. In fact, many police entry teams have gone to handguns for entry, for greater manuverability inside structures.
I think that the funds to buy either of these long guns may be better spent on more handgun training.
And I do believe the AUG is the finest 5.56 rifle extant.