The Mossberg is a sturdy reliable and inexpensive shotgun, and I wouldn't be surprised if it outsells the 870. That said, the Wingmaster and the Ithaca M37 (old version) and of course the Winchester 12 are three trombones that I have very genuine reverence for.
Other guns I would put high on the list of guns that everybody owns would be Rugers .22 pistols, both single action and autoloader.
They say in the survivalist books that if it ever came a national combat here the the three “must own” guns are a good 12 ga, a 22 cal rimfire, and a 30/30 winchester.
I was surprised at the latter but it said there is more 30/30 rifle ammo sold here than any other caliber.( except 22 rimfire)
In Canada it said you are better off with the 303 British because its #1 there in rifle ammo.