The best choice for protection is not high volume of fire, because if you find yourself in such close quarters with your enemy, somebody screwed up BIG TIME!
What really matters is, using a weapon that is capable of taking out their brain stems from 1,000 meters, where they can't tell where the shot came from or see the shooter.
That kind of accuracy and range has no match, and using your ammo carefully and effectively also has no other rivals. In the coming future, if the World ever does find itself wrapped in Anarchy again, One-Shot-One-Kill will be the only motto, or “Silent souls leave .308 holes.)
And the AR-15 is not even remotely capable of that tactical advantage.
Remington model 700 BDL, accurized and custom tuned, in the very least 7.62 NATO (308 Win.) or better yet, 300 Win. Mag., will prove to be the best choice every time.
Close work means some one screwed up may be what we wind up facing so a semi-automatic that is easy to field strip and clean and where ammo is plentiful will have to do for me.