Well, lucky thing about my job is I get to see lots of dead people! :shock: You see, I'm a Deputy Coroner.
I've had the opportunity to see, first-hand, several people killed via shotguns, exclusively with various shot loads (no buckshot or slugs). All of them were contact wounds (self-inflicted).
First, let's get one thing straight: Unless you reside in the Taj M'Hal, you're longest home defense shot is going to be at or less than 15 yards. At this range, even with an open-choke shotgun, the shot load is not going to spread out much. So, Rule #1 with a home defense shotgun: Shoot it like a rifle, because you MUST hit vital organs to stop the attack.
Next: Birdshot is very effective at not overpenetrating. Example: Had a fellow shoot himself in the chest with a 12ga. 1-1/4oz. load of Hi-Velocity #4 shot. This was a contact wound. The shot did not exit his body. (The human epidermis is extraordinarily elastic.) After the shot charge went through his body, destroying a very narrow path of tissue (most of the internal damage was caused by the powder charge which had nowhere to go, except inside him, since there was tight contact between the muzzle and the skin), the skin on the back side of his torso stretched out and "caught" the shot charge. The shot was all laying in between the epidermis and the sub-cutaneous fat layer on his back. So, Rule #2 with a home defense shotgun: If over-penetration is a worry, birdshot is a good choice for a defensive load.
Next: Another fellow shot himself in the head with a shotgun. (1oz of #7.5 in a 20ga. if I remember correctly.) This completely removed the skull cap and spread his brain over the ceiling. Rule #3 with a home defense shotgun: Rule #2 only applies if you shoot the badguy in the torso, where the skin can stretch. Refer to Rule #1!
Lastly: A case that really stands out in my mind was a baffler for awhile. There was a blood trail leading from a residence out into the back yard where the body was laying. There was a spent shotshell hull laying in the grass, along with the body and a shotgun, which still had an additional spent hull in the chamber. We thought we had a homicide at first, until we looked into several details. To make a long story short, this chap had shot himself with a 12ga (#6 shot this time, can't remember how heavy, but probably 1-1/8oz.) in the chest, BUT, he hadn't read Rule #1 above, and he missed his spine, heart, aorta, one lung, his liver, and his esophogus. Rather than lay there, suffering, waiting to bleed out, he crawled 35 yards back into the residence, grabbed two more shells out of the box, which was still on a shelf, several feet above the floor, and then crawled back out and finished the job. So, Rule #4 with a home-defense shotgun is: ALWAYS remember Rule #1!
I think we take for granted that if we get out the street howitzer, and start pulling the trigger at badguys, it doesn't matter where we hit them. Oh CONTRARE!! It matters MUCH MORE where we hit them, than whether we hit them with birdshot, buckshot, or a slug. Please, for your own sakes, remember that if (God forbid) you ever do have to defend yourself, remember: SHOT PLACEMENT!!!!
Now, for my own preferences, I load #1 Buckshot for home defense. It's the Winchester 20-pellet load at 1075fps.