As to shotguns vs rifles.
I teach a weekly ladies firearm safety and self defense class.
Just after Uncle Joe came out with his "all you need is a double barreled shot gun" rant the ladies asked me about the shotgun and or rifle.
I wouldn't tell them, instead I brought a shot gun and rifle to the class and had them try them both.
EVERY lady in the class did better with the rifle. They didn't like shooting the shotgun because of recoil (and I was using light trap loads). This was an in door range so I couldn't use an AR but instead I let them shoot a Marlin 94 38/357. Now that its warming up I'll take them outside and let them try the AR.
What I did was had each woman measure their house, figuring the farthest distance they would shoot. Some had smaller homes so the spread of the shotguns wouldn't be a problem. A couple had larger homes and the spread would put others in danger even if they hit the bandit.
All had no problem getting good hits with the rifle at normal SD shooting in the home.
One scenario was to pretend that the bandit got one of their kids and held them as a hostage. I have a hostage target for them to shoot. NON had any problem hitting the bandit portion of the target with the rifle. You can guess what happened when it was attempted with a shotgun.
When you try to choose between a shotgun or rifle, instead of going by what's said on the internet, get one of each and go to the range and see for your self. Take measurements of you home and use that distance to set up your targets.
I like the M1/M14 but they are over kill for SD. AR, or carbine type rifles (Marlin/Henry Levers) are a different story altogether. Also the M1 Carbine, but they are getting hard to find at reasonable prices. AR's are fine, just look at how many more women and juniors have gotten into and are doing great in High Power Matches since the AR's replaced the M14/M1A's in those matches.
Before you buy a dedicated SD rifle/shotgun, go out and shot one, take your wife or who ever else may have to use it out and see if they can shoot it.
Most women don't like shotguns and face it, we may not be home and self defense may be left to the Misses.
Don't tell anyone what is the best SD rifle/pistol/shotgun for SD, we're all different. Give them a variety of choices, let them shoot them based on their situation and what they can shoot best.
An example, someone mentioned rural areas. I live in a rural area, I can shoot a long ways. I'd be perfectly happy and feel save with a bolt gun.
Come visit and watch me shoot a M1903A3 with stripper clips and then tell me its too slow. But not everyone practices rapid fire with a bolt gun and fewer yet use stripper clips. Having said that, I feel perfectly safe sticking to my J-frame. Not sure you can justify a 600 yard shot as self defense.