For home security, at the "room" range, most any quality shotgun is going to have adequate accuracy. What you're probably more interested is in pattern and spread. Those things vary per gun and round loaded.
As for the best quality, almost any of the major brands make products that function and feed reliably. As for secondary quality things i.e. fit and finish, it's whatever you want to pay for. Honestly, for home defense, you're probably not going to notice MUCH difference between an entry level Mossberg and a BenM-1 unless you really shoot a great deal or compete.
Very few people would argue the suitability of an 870 or Mossberg 500.
If you mean "short barrel" better than long barrel, only for moving around. If you're in a room watching a door, it's pretty much a non-player. For defense, even if you're going to "fortress" up, having a shorter barrel is handy for the "what if" situation that's bound to pop up.
Another thing about a short barrel shotgun is that it's easier to hide and retrieve . . . especially when you're in a hurry.
Pros: short, one could argue faster to move around
Cons: recoil can be excessive; the follow up shot is a lot tougher
For a home defense gun, I see little or no reason for a pistol grip only shotgun.
Shotguns are seen by many as the holy grail of home defense, and there are good reasons why. The shotgun is intimidating, and the sound of that slide racking is not what you want to hear in the middle of the night. No one is going to argue the effectiveness of modern self-defense buckshot loads, either.
That being said, shotguns have some drawbacks as your INITIAL home defense weapon. The biggest drawbacks I see is size and placement. Typically people put a shotgun in a closet or some other storage area. Yeah, some can put them under or beside the bed, but that's not always practical (or safe). A handgun, on the other, eh, "hand", is very easily stored and hidden away. It's also faster to employ, even if marginally.
What I think one has to do is consider the scenarios in which a defensive weapon will most likely be needed. We all think of "the bump in the night" scenario where we hear someone creeping in. You get up, grab your shotgun, and prepare. What happens, though, when the "bump" is coming in your bedroom door? Having the 9mm in the drawer for immediate action is better than the shotgun under the bed or in the closet.
Another drawback a shotgun has is that it's difficult to place around the house in case you feel the need to have it handy. Let's say it's a "dark and stormy" night, and you're cooking dinner. Hanging your Mossberg up beside the fridge may be a bit . . . weird, but tossing your Glock or Ruger in the drawer beside the stove is easy enough.
I feel, believe, whatever that, for home defense, a handgun should almost always be the first purchase. Depending on the size and layout of your home, TWO handguns may be called for. You never want to be between an entry door (from the outside) and your defensive firearm, so you may need 2 handguns.
After you have that covered, a shotgun is a fine second line of defense for your home, and what I mean is the shotgun is what you grab AFTER you've secured your immediate safety with a quick response handgun.
For defensive work, 12 or 20 gauge is fine. Actually, for indoors work, I REALLY like a 20 gauge. At that range, it's dern close to a 12 gauge, and TYPICALLY it has less recoil, muzzle flash (think "I'm blind" after your first shot), and noice (think "I'm deaf" after the first shot). For 12 gauge, I like #1 buckshot, but "0" and "00" buckshot has been used for years. For 20 gauge, last time I checked it was available in #2 and #3 for good defensive work. I'd steer clear of "birdshot" as it does not always penetrate reliably enough to bet your life on.
Whatever you pick, go shoot it with defensive loads. See how LITTLE the spread is at room distances. Also, if you can, shoot it at night. Heh, if you can, get some plywood and build a little hallway. Shoot it there, at night, with no ear plugs. THAT'S what it's going to be like if you have to really do it. THEN you might want to reconsider loadings. :)