I like post #2, the one in your hand, but my gun of choice is a pump shotgun. Mine happens to be 16 gauge, because I got a good deal 30 years ago. At home defense range even if I run out of buckshot, the #5 shot I also have will do the job. 15 feet away it’s still less than a foot wide pattern. Bird shot would work.
More recently I snagged a 9mm, which one I would grab depends on whether I have time to plan or have to grab and fire. In a pinch, it’s the shotgun. Last thing a burglar wants to hear is when I rack one into the chamber. That’s why it’s the only one in the house without a round already there.
For the beginner, definitely shotgun, and get some practice using it. A pump can fire almost as fast as a semi auto, if you know how to use it. I’ve been called on that one, I can back it up.
You want to know how freakin LOUD the thing is, and how hard it hits your shoulder. I fired a 22 pistol in the cab of a truck one day. (22 Llama semi auto, snake in a ditch). Sounded like a damn hand grenade...didn’t do that again...
Why wouldn't you recommend a semi-automatic shotgun? You would think that a home invader, running around the room and throwing things at you might cause you to miss. A quick pull of the trigger for the second shot would be more likely to get them.
Good against remotes, that's one thing. Good against the living?
Pump operation, whether you "know how to use it" or not, is a lot harder during an adrenaline dump.