New to the site, but not new to being prepared. Just a few comments based on my own opinions and practices. As a current L.E.O. I've gone the route of going with:
What I know.
What I've trained with.
What I feel comfortable with.
There is a tremendous amount of great and well intentioned information on this site, but when the time comes it will all come down to what works for you, the individual, and those loved ones that you are responsible for. Here's my take on the Calibers for Survival. Firepower is how many times you hit the target, and not how many rounds you have. You can have all the bells and whistles available on the most exotic and expensive weapons platforms, but it will be nothing but noise if you can't hit your target. Firing a weapon is a mindset, and an extremely perishable skill. Are you prepared to shoot, and can you shoot are the two biggest questions that need to be answered. If the answer is yes, then any individual is ready to take that important step towards self sufficiency.
Here is the personal route I went for my family and I.
Pistol Calibers - 40 cal. It's what I know and what I train with. It's readily available as it is one of the most common L.E.O. rounds in use. It has knockdown power when placed appropriately, and can be obtained at a decent price. My weapon is the S&W M&P 40 in full size and compact. Good solid weapon.
Shotgun - Mossberg 590 12 ga. Things shot with a shotgun tend to stay shot. Nothing more to say really. "OO" and slugs for me.
AR15 - S&W M&P15. Lots of people argue when it comes to what they'll take into battle. I prefer this as it's user friendly, accurate, and reliable. No gimmicks, bells, or whistles. Iron sights rule when Murphy's Law pays you a visit. The bad thing is that ARs cost money, so that could be restrictive for many.
Marlin .22 - Everyone should have a .22, and you can buy thousands of rounds for what it costs to takes your family to the movies these days.
Mosin Nagant M44 - Best kept secret when it comes to a reliable weapon that makes a huge BOOM when it goes off. These are readily available at a good price. You can stock up on them, and outfit an entire family. The M44 fires the 7.62x54R round. Ammo is easy to get a hold of, and the weapon will serve you well.
Bottom line .... I'd rather get missed 30 times with 7.62 than hit once in the face with .22. Do what works for you, your situation, your budget, and your abilities. Most of all....be prepared.