I had kept #4 buck in my HD pump for a long time. Inside the home and at short range, it's a fine round. Recently however, I have switched to #1 buck for my first couple of shots, followed by #00 buck. I never see #1 buck at my local sporting goods stores, but it can be found online.
I began to reconsider #4 buck after reading an account of a police officer, who used this shell in a shoot out with a bad guy. Long story short: the bad guy was hit center mass at 35 - 40 yds. The bad guy was wearing a heavy leather jacket. Not one pellet penetrated into a vital organ.
Now I don't think it prudent that any civilian follow a bad guy outside of your home. Make sure your family is safe, call 911 and wait for the Calvary to arrive. But after reading that LEO's account, I thought a shell with a slightly larger and heavier pellets might be the way to go.
Apples and oranges my friend, there is a big difference between 20' or less inside your house at dark thirty and 40 yards on the street. Longest possible shot in my house is 8 yards but I practice my Defense drills at 8 yards to 25 yards with multiple targets with both of my home defense shotguns. 0 or 00 or 000 would be better but in my house that is contraindicated by my house layout and occupants so I opted for #4 birdshot after some experimenting and patterning. Not what I would use for outside the house but I have handguns and rifles for that eventuality if need be and it doesn't take me long to load a handful of slugs if for some reason I determine a shotgun would still be the better choice. It's good to have options but for those who don't have those options, (they may be limited in resources and supplies), so you gotta use what you got, use it as well as you can, keep your cool and don't panic if the bad guy does not fly backwards through the air for 20'.