To paraphrase Jeff Cooper, a gun isn’t the magic wand portrayed on TV that resolves bad people by simply waving in their general direction.
Buying the cheapest one on the Walmart rack - or a $2000 tacticool M4gery for that matter - a month before a crisis and locking it up in the closet just in case is only marginally better than doing nothing at all.
The time to go out in the woods and plink is today. When making every mistake in the book doesn’t matter.
Bingo.
IMHO, the primary issues to consider are: (1) does the firearm function properly and safely, (2) is the person comfortable using it, and (3) has the person practiced, practiced, practiced with that specific firearm.
Just about any firearm purchased from a reputable dealer will pass (1). (2) and (3) are up to the person.
For example, lots of people poo-poo .22s, and frankly for good reason. However, a .22 that someone is comfortable firing is vastly superior - for them - than a .357 mag they’ve not practiced with and are not comfortable firing.
All that said, lots of good choice/selection advice above. My personal choices: .357 mag six shooter on the hip and 12 ga pump shotgun in hand for close quarters. If things really go bad, I’ll shift to my scoped AR-180B with multiple 30 round clips and Sig 9mm with extra clips. If things go further south and I’m still in the $#!+, I might bring out some real artillery. Some here will criticize the AR-180B and 9mm as not having enough stopping power (tend to punch holes). Their points have a lot of validity. However, those are the firearms with which I’ve put in the most time practicing rapid (for me) aimed fire, so that’s what I’d go with.
I also plan to be at a friend’s place on election night - someone I shoot with regularly and can trust. He’s armed for bear, too.