Premise has a logical flaw in it from "our" perspective.
"We" generally understand that small service-caliber firearms are more "polite" for every-day carry. "We" will also likely have a "full size" sidearm, and probably a carbine of some sort for actual HD.
Which is probably not what will be best for "one gun only" households. A G19 or a G19, and M&P, a Dagger, any of that will likely suffice for such use. For that matter, so would a .38 or .357 revolver, or even an 1911 of some stripe.
For the neophytes and noobs, I usually bore the to tears on the topic of how your "carry" is a "last resort," something you fall back upon only after everything else has failed. That, in a "gunfight" it's likely the guy with the rifle that wins (and has the advantage of making bad people stay much further away, too). And, yes, that's all tough sledding at the best of times. Tough enough for "us" as well, like as not, too.
If a newbie insists n "What one gun should I buy?" I usually send them to the LGS and tell them to get a 16" S&W M&P carbine. Can they "carry" that--not in the general sense "we" mean, but likely "yes" in the way "they" mean. If between today and that putative darker time, they need an EDC, they can go and find what suits them best. Preferably after getting experience and trigger time.
Pistol skills atrophy fastest, and specialty pistol often faster than general pistol. Better to give the newbs an easier learning curve, and let them advance from there.
But, that's my 2¢, others' will differ.