Best Survival Weapons

The conversation that came up today is "What are the Best Survival Weapons?". There was an overwhelming pool of opinions from conservative to exotic. Doing a quick search on You-Tube brings about a bunch of uninformed and mostly uneducated guesses on what makes the "Best" survival weapons.
First off, let me explain one thing. A firearm is a tool. And just like any other tool, each has its own uses and purpose. You cannot say that a hammer is the best tool to build a house, because you still need a saw, a level, and few other items to properly build that house. The same can be said of firearms. There is no one firearm that is the best for every situation. Each has its own uses, and all are useful when you have nothing at all.
Now, let me explain my list and why I'd pick each one. After that, you choose your own tools. By the way, my list comes from firearms that are actually obtainable. You will not see a Vulcan or a grenade launcher on this list. Although useful, if they came to your mind, you either have too much money, or your sitting in your moms basement playing Call of Duty III.
First off, IF I could only grab one weapon. Meaning, if I only had time to grab one of my weapons and flee my home never to return, I would grab a 12 gauge, pump action shotgun.
Now the reason for this choice: The 12 gauge shotgun is arguably the most universal tool. It is the best defensive weapon for short to medium range. You can use #8 shot for small birds and rabbit sized critters. You can use 00 buck for the larger animals including the two legged kind, and then you have the option of the slug which can take game to the size of an Elk or a black bear. Ammo of all types for the 12 gauge is reasonably common.
Now the first thing an inexperienced shooter wants to do is cut off the barrel and put a pistol grip on it. DONT! While this may be great for defending inside your home, it makes it no better than a pistol for anything else. Cutting off the barrel seriously affects the effective range, and adding a pistol grip makes it not only unwieldy but dangerous to the operator. There are lots of examples of people breaking their own noses or worse by trying to aim a pistol gripped shotgun.
My second choice. Meaning, if I only had time to grab 2 weapons, and the first was the shotgun. My second grab would be a pistol. This is where the grey area is, because everybody and their brothers cousin has a strong opinion on what is the best pistol. Even I have a hard time deciding which one I would go with, but with much thought and even more debate, I would grab a high capacity 9mm. I can hear the hiss's now from all the .45 lovers out there, but that is my choice.
My reasoning for a pistol: You can't always carry your shotgun. There are times when your digging a ditch, using the latrine, or sleeping when you cannot actively hold or sling your long weapon and still function. A pistol is always handy in a holster at your side. A pistol, as a tool, has one job: protect you long enough to get to a better weapon. Period. A pistol is a under-powered tool meant to be used only when nothing else is available. My reasoning for the 9mm is: It is the same caliber that the US Military and many police departments use, making ammo obtainable. The 9mm round has its own ups and downs. The downs are that it is fast and may "over penetrate" your target hitting someone behind them. Also, it may not have the knock-down power of the larger .40 or .45 caliber rounds. The benefits of the 9mm is the high capacity of the firearm. When your using your pistol, your only using it to stop the threat long enough to get to a better weapon. 16 shots from a 9mm while your running for your shotgun may buy you that time. Yes, they are making high capacity .45's now, but the extra weight of the pistols when your not using it vs the benefits swayed me to the 9mm in a combat situation.
My third choice. The venerable .22 caliber rifle. The .22 is the supreme survival rifle capable of providing meat to your table for years. You can carry 500 rounds of ammo in one pocket, and it is accurate enough to provide you with a small meal for every one of those shots. I have seen coyotes knocked over backwards by it, and deer dropped with one very well placed shot at 100 yards, although I do not recommend this in any but dire circumstances. Any dependable and accurate .22 is a good choice. You can find ammo between seat cushions in vehicles and even in the junk drawers of some homes. Even though it is 3rd on my list, the .22 is the one I will depend on most for the long haul.
My fourth and fifth grabs would be a light and heavy assault rifle. Examples of a light rifle would be a AR-15(M4) or AK47 type weapon. A light rifle is one that shoots a medium sized cartridge and is effective from short to medium range which is considered to be 300 meters. Generally, with a large magazine capacity and capable of sustained, controllable fire. There are almost as many arguments over a light rifle as there are pistols concerning which is the best. In my opinion, the best one is the one that saves your life. I started writing a big long debate over what is the best light assault rifle, but after typing it out I realized that it is a debate you should make for yourself. They all have their own pro's and con's. The idea of a light assault rifle is for defending a position. Continuous, well aimed firepower upon your assailants until they are dead or give up the attack. If you run out of ammo, or cant keep their heads down to keep them from firing on you, then its game over. They also make great hunting rifles for deer sized animals, are easy to carry, and ammo may be fairly common.
A heavy assault rifle is one that shoots a large cartridge and is effective to at least 500 meters. Examples of this are the Cetme or the AR10 Style Rifles. Their heavier and faster bullets are capable of penetrating though walls and cars while still maintaining a sustained, controllable fire. The general principle of a heavy rifle is the same as the light rifle except that while your companions keep the assailants hiding behind walls and cars, you can take careful aim and shoot through walls and cars to take them out. The .308 cartridge is an excellent choice because of it accuracy, its power, and the availability of ammo. The weapons and ammo are generally heavier than their light duty counterparts, and the magazine capacity will be limited, but the extended range and power makes up for it. They are capable of taking down any North American animal.
In summary, I tried to keep this as general as possible. A shotgun, pistol, .22 rifle, light and heavy assault rifles. Buy what you can afford, then upgrade from there. Having a weapon in hand is better than money in the bank if you should need it. I have my own opinions on which brand is better, but I may just leave that for another time. What is important is that you are able to defend yourself and your loved ones when the need arises.