I vote for the 870.
This is a discussion on Recommend a HD Shotgun within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; I vote for the 870....
I have shot bad guys with buckshot and bean bag rounds as well as breeched doors with my Mossberg 590 and I would not use any other shotgun, well except for the mil spec 500 that is the first floor long gun.
My agency issued 870s but most guys bought their own 590s or 500s. Make sure you get a light.
By the way, here's same gun, Synthetic Express 7 round, stock except for jury rigged flashlight holder.
Oh, and they hold 6 rounds in tube (2.75" shells, one less if 3" shells), +1 in chamber, not 7 in tube:
I have the 870 express with the stock extended mag tube (7 shot).
I added a vangcomp big head safety and will be also adding a light.
If you're a lefty, like me, the 500 is the way to go. The ejection won't matter, but the safety is a lot easier to use. Use whaterver stock you like that feels comfortable, but beware of butt-mounted shell carriers. If you look at the SPT 500 in the pic you'll see that sharp, hard plastic shell holder will be right on your cheek. Same for the righties, your house may have a place of cover or a corner where you might have to go lefty and those things will literally break your face. just about everything you can get for the 870 you can get for the 500. Not that you need a lot. A shell carrier or sidesaddle, maybe a light, maybe a big dot bead or a nightsight. I use California Comp. Works belt mounted shell carriers and a Trijicon front sight. Got a big bead on the wife's 500 (.410) Most of the rest is gadgets and tacticool fluff.
Frankly Remington, Mossberg or Winchester pumps are all good I guess, just depends on what you like. Ford v. Chevy?????
You can also pick up a used 1200 or 1300 Winchester defender real cheap on Gunbroker these days if you look. They don't get alot of press or respect but they are/were well built guns.
When you've got 'em by the balls, their hearts & minds will follow. Semper Fi.
Abort the Obamanation not the Constitution
Those who would, deny, require permit, license, certification, or authorization for me to bear arms are as vile, dangerous & evil as those who would molest, abuse, assault, rape or murder my family
The agency I currently work for, and the one previous to that, both issue the Remington 870. That would be my choice based on what my employer issues and training.
Another option is a Hatsan Escort. It's a cheap Turkish "copy" of a Remington, if you don't want to get a used "police trade in". Personally, if this is to be a weapon used by you and your spouse, significant other or visiting Uncle Fred, I'd look long and hard at a 20 Guage. "Pool Weapons" need to be able to be used by the least able of your "pool" of potential weapon users.
I also like the Coach Gun idea. Like a Revolver, then gun can be completely "at rest" while loaded. You could load it, stick it in the closet and come back in fifty years and it would still function properly. That may or may not happen with any Autoloading or Pump Action Shotgun.
I forgot to add that I'm a lefty too, and outside of a Thumbhole Stock and Holsters, I doubt I'd recommend a left handed anything to somebody as it is relating to firearms.
I do recommend Ambi Thumb Safeties for Hi Powers and 1911's though.
Another lefty, I use the 590A1 simply for the fact that its got the tang mounted safety.