A shotgun is a good tool to have around, IF....
One actually likes shooting it. Back when I instructed heavily for the State of Md's Correctional System, I found that no rookie moved past bare minimum competence unless they shot a shotgun recreationally, and the more they shot, the better they did, regardless of game or sport. IOW, a trapshooter, with his/her ritualized game and specialized equipment, shooting twice weekly, was oddson better at "Serious" shotgunning than a casual hunter who shot at doves a few times a year and maybe a goose hunt or two.
ANY reliable shotgun of at least 2 shot capacity and 20 ga or more is an incredibly effective close range defensive tool in trained hands.
And that's right out of the box, no bells, no whistles. While there's a lot of old threads on this with great input, here's a couple of parameters IF you're willing and able to put in the time and committment "Serious" shotgunning requires.
Length, under 4 feet, 40" is better.
Capacity, at least two shots.
Sights,whatever works for you.
Action type, see above.
Trigger, clean, safe and under 4 lbs or so.
Stock, any full length(No PG onlys) stock that FITS.
And plenty of ammo.REPEAT, plenty of ammo. Use up, buy more, do it again.
There you go, no bells, whistles, fuzzy dice or fender skirts. No lazers, belt feeds, bayonets,or super 3 1/2" shells loaded with depleted Uranium 000 pellets rubbed with garlic.
And, while my "Serious" shotguns are 870s with lots of accessories, every single piece that's been added has been added after establishing a need,rather than a want.The mag extensions are there as much for kick control and slug group tightening as for any hunch I have that 6 or 7 rounds of shotgun ammo will get me out of an AS scenario that 4 rounds won't.
I could go shoot my old agency qualifier with an absolutely stock 870 and score over 90%. With the gadgets added, maybe 95%, at a guess.
And,dunno if a tyro needs Gunsite level instruction, but it can't hurt.Sufficiently advanced instruction at the beginner level may be available closer, cheaper and more accessible.
As for choice, the 870s are hard to beat. Get a used one, they last forever, and QC may be slipping in these PC times...
Any questions, sing out.....