Spent the last six months researching HD shotguns TO DEATH,
Read over 100 on line reviews and watched more YT reviews of most pump and semiautomatic dedicated 12 gauge HD/Tactical shotguns than I can recall.
Watched literally dozens of birdshot VS 00 buck VS #1 Buck VS #4 Buck penetration tests
Which kind pump or semiauto and what manufacturer is 100% dependent on what YOU WANT the gun to do.
I would absolutely stay away from the "economical/affordable" magazine fed semiautomatic shotguns mostly for reasons of unreliability but also reasons of practicality and increased liability in a post self defense shooting civil lawsuit. I own A BUNCH of pump and two semiauto shotguns and have fired countless thousands of rounds from them and knock on wood had only ONE fail to work when its ultra cheaply made factory plastic shell fallower wore out and started causing failures to feed. I have watched way to many videos on magazine fed 12ga shotguns to ever trust one with my life or the lives of my family.
I live in a city so overpenetration of a projectile(s) from a firearm in a home intruder self defense situation fired inside my home that finds it's way outside of my home is a VERY VERY real concern of mine. A 12ga shotgun shooting a 1-1/4oz of buffered #5 bird shot using a Improved-modified choke is based on my own test firings is a VERY effective defensive round at any shot distances I measured I will encounter within my home. I duplicated Paul Harrells test using Winchester, Federal and Remington high velocity heavy upland game loads and a 1-1/4oz load of #5 bird shot in the center chest of any home intruder will immediately incapacitate him and #5 birdshot unlike 00 buckshot, 45acp or .223 has a significantly lower risk of blasting it's way through my interior walls to exit my home and continue in flight and injuring an innocent bystander.
In MY OPINION if projectile(s) over penetration is a risk to serious to ignore and your budget is somewhat limited, your best choice from the viewpoint of economics, civil and criminal liabilities is buy a highly reliable purposely designed for home defense shotgun like a Mossberg 590, 500 or Maverick 88, or if you can find one in very good shape a used Remington 870 Express Magnum Tactical.
I live in a state if an act of self defense is judged by police to have been justified you can not be sued in civil court buy your assailant or if deceased their family. But in many states across America you can and odds are will be sued in civil court by your attacker of if they are deceased their family and inescapable fact is the scumbag lawyer representing the plaintiffs will show the jury the weapon you used to justifiably "un-alive" the home intruder and a plane jane looking 12ga shotgun has a much better chance not to prejudice members of the jury against you like an AR-15 just might. Also I only drive on my vacations and plan on packing along my HD shotgun especially if truck camping and unlike an AR-15, a basic non-pistol grip shotgun is legal in every state I will ever camp in or drive through.
My testing found there is just to significant to ignore of an advantage in a dedicated home defense/TSHHTF shotgun using either a Improved-modified choke or a full choke shooting birdshot, #1, #4 and 00 buckshot for me to buy a shotgun whos barrel has a fixed improved cylinder or cylinder choke, any shotgun I buy MUST absolutely have a removable choke system so I can maximize that guns usefulness as both a HD/tactical shotgun and as a effective mid-range hunting or defensive gun using Foster slugs.
I just recently shot high quality buffered 12ga 2.75" 8 and 9 count 00 buckshot shells at 10, 15, 20, 25, 30 and 50 yards and using a Improved-modified choke literally cut my pattern size IN HALF at all ranges VS using a IC choke and eliminated over 90% of the fliers I was experiencing at 25-50 yards.
So my advice is if your budget is somewhat limited buy a 20" 8+1 Mossberg 590 with ghost ring sight system as it features Mossbergs proprietary Accu-Choke removable choke system.
I recommend the Mossberg 590 over the 500 because they are so close in price might as well get the better HD shotgun.
If you are on a very tight budget the Mossberg Maverick 88 is a great solid HD shotgun with proven reliability.
If you want a shotgun what has a pistol grip and all steel ghost ring sights and a factory picatinny rail then look at the AakKar Churchill 612 tactical. Its essentlually a clone of the Remington 870 Express but is different in some ways. I have one and for less than $230 it is an amazing bargain. I have fired 200 shells through mine with zero issues so far and plan on doing a review of it soon.
If you MUST have a semiautos HD shotgun an can afford about another $350 to $400 more than the price of the Mossberg 590 again in MY OPINION the best semiautomatic HD shotgun under $900 OTD is the Beretta A300 Ultima Patrol. YT is littered with reviews of the Beretta A300 Ultra Patrol and they are 90%+ positive.