Terminally speaking; handguns are the least effective at stopping a determined threat instantly, or within a few seconds.
Handguns are however the only weapon easily maneuvered/manipulated by a single hand, leaving the other free for additional tasks.
PCCs still don't get the velocity high enough (2,200 FPS or more) to create the additional crushing/tearing of tissue outside if whatever the bullet comes in contact with. The only thing the PCC has over the AR is significantly less muzzle flash and report...but that comes at a cost of lethality.
00 buck will exit the human body with at least some of the payload, so downrange considerations are necessary. It will also penetrate interior and most exterior walls more than a 55gr .223 FMJ/non-binded soft point etc... However, for a single trigger pull there is nothing potentially more lethal at closer ranges.
The AR requires either a suppressor (added weight and length) OR experience shooting one without hearing protection. Having touched off an M4A1 indoors without ear pro, it is not something that will shut you down because of the adrenaline rush...but your ability to communicate is reduced as is your situational awareness. Long term hearing loss is also guaranteed...but in an HD environment that is a pretty easy trade-off.
Once you go larger than .223/5.56 over penetration becomes a bigger consideration.
I personally am a big proponent of having more than one option, especially living out here in the country where a 911 call will take 45 minutes. My AR is loaded with 55gr bonded soft points, and my shotgun with #4 buck. Having family in the house I have to balance lethality with penetration concerns. Fortunately, both are extremely lethal at closer ranges.
No situation is a one-size fits all here. There is no universal "right" answer...but there are universal wrong ones.