Ah, the question. It's come up indirectly a few times recently as I've talked to people that I know, and it's a good question, seeing as how not all guns are created equal. Let's face it, aside from sending lead downrange, there are differences in size, power, magazine capacity and action type as well as intended purposes for which they were designed. I mean, I love my M60 and consider it a great tool, but it's not exactly concealable, nor is it precise enough to use for long-distance game harvesting. Truth be told, it's really only good for denying people access to select terrain on defense or on the advance, keeping their heads down while flanking riflemen advance. Otherwise, it's not terribly handy other than at machine gun shoots and trips to the range when I feel the need to show off. The same can be said for most automatic weapons and other firearms like the .50 BMG rifles.
For regular use though--hunting and self-defense in typically expected situations--most of the experts out there recommend that each gun owner have a basic battery of four guns: A shotgun, a pistol, a centerfire rifle and a .22. I confess to having a tad more than four guns here at the Lair but that's only because I'm indecisive and can't pick just four. I agree with the logic, however, because that four-gun battery can enable the shooter to do most anything from harvesting game of all sorts to managing his/her defense in both close-in and long-range situations.
So let's look at a few choices here.
Pistols. Pistols are great. Everyone should have one, I think, except for felons, the mentally ill, and people who insist on voting for Obama the second time around. (But I repeat myself.) While not the best choice for hunting and generally not phenomenal man-stoppers, they're concealable, quick to bring into action and a great alternative to screaming "please don't attack me!" The caliber choice in pistols is enormous, ranging from the silly and ridiculous on the small end, right on up through a range of excellent choices, and reaching right back to silly and/or ridiculous on the heavy end of the spectrum. .22short or .25ACP as a defensive arm? Well it beats nothing, but not by much. And .454 Casull or .50AE are just too big and recoil too fiercely for most shooters to try to pack for protection when going downtown for a show. But that range between .380 (arguably) and .357 Magnum is going to work pretty good for most people. I usually always have something along those lines on me when I'm out and about, and at home, one of them will be used to fight my way to the gun safe where the rifles are when things go "bump" in the night. Any and every gun owner serious about defending him/herself and/or their loved ones should have a pistol and become proficient with it. Ideally they'll have a well-made one in a caliber that's common and easy to obtain in emergencies. I love my .41 Magnum but the local gun shop doesn't stock rounds for it on a good day so it's probably not the best thing for me to rely on in a crisis.
Shotguns. Mas Ayoob likens the defensive shotgun to artillery: they put a lot of firepower into a pre-designated area, and as defensive tools, they're hard to beat. They also have the advantage of being able to fire shot of all sizes, from #8 birdshot to 1oz slugs. As a game-getter, few things beat the shotgun for putting meat on the table, be it bird or beast. In a survival situation, this could mean the difference between making it through the winter or starving to death. The versatility of this firearm is unmatched and no home should be without one, particularly in rural areas.
Rifles: Way back to the days of the early Americans, it was envisioned that every man have a rifle, both for hunting and military use if need be. Back then it was the muzzle-loader but today the choices are pretty much endless. I recommend sticking to military calibers as they are the easiest to come by, and a proven semi-automatic platform will make more sense as a fighting rifle than that bolt-action rifle that you got on sale at Wal-Mart. Yes, that Remington Model 700 is a nice rifle, but it was intended for the fellow who plans to shoot a box or two of ammo all year, not the guy sending rounds downrange until the finish cooks off of the barrel. The AR-15 is probably top dog today in the lighter fighting rifle category due to it's size, reliability, and commonality, but those preferring a bit more range and punch have many rifles to choose from in calibers like 7.62x51 (.308) or even .30-06. Yep, that old M-1 Garand, if properly maintained, will still serve a shooter well today as a defensive arm and a harvester of large game.
And then there's the "lowly" .22 rifle. Some armchair commandos mock the idea, but the little .22 has it role, too. It'll take rabbits, squirrel and similar small game animals without destroying the meant and/or telling everyone for five miles that you're there, and it's a great training tool that you can use to brush up on your marksmanship or teach others the fundamentals. There's really no excuse not to have one around, and in a survival situation, a good one will be worth its weight in gold.
Now with those basics set out, people can, will and have argued ad infinitum about which ones are "the best". If not for choices and differing opinions, most gun magazines would have nothing to produce articles about. I won't even try to to tell you what you should have, but I'll explain my own choices and recommend that if you haven't made your own selections yet, that you do your homework and make some informed choices based on what works best for you.
Pistol-wise, I'm happiest with my Model 1911 .45 Automatic pistols and 4" .357 Smith and Wesson revolvers. But then I'm old and not horribly imaginative so I find comfort in things that have always worked before. The designs are proven and reliable, the ammo widely available just about everywhere, and the power is sufficient to do what a handgun should do: stop a close-in immediate threat.
That said, there are many wonderful pistols out there in 9mm and .40 and even some decent .380s. The one that will be the best for you is probably going to be the one that you shoot the best, all other things being equal.
For a shotgun, I love the Remington 870 pump in 12 gauge. It's a proven design, tough and reliable, and 12 gauge ammo is the most common shotgun ammunition available. I also trained with and qualified on this weapon for a number of years and am intimately familiar with it, so that's a plus for me personally.
Rifle-wise, I just never could decide. I've got a lot of them, but come the bad times, I think that I'll be settling on an AR-15 carbine and my M-1A in .308 for that added smack at longer ranges. But if you're fond of the H&K platforms in either .223 or .308, the Ruger Mini, the FAL, or even an M1 carbine or an AK platform, good on ya so long as you're familiar enough with it to operate it by feel, hit what you aim at at various distances, and fix it when it breaks, as all thinks mechanical do. remember also that in any semi-automatic weapon, the magazines are it's heart and soul, so make sure that you've got good ones and plenty of them.
As for .22s, One of my very first firearms ever was a Ruger 10-22 that I got not long after leaving high school. I still have it and it's seen thousands of rounds fired. I know it like few other firearms and would trust it with my life.
Now as to ammo, this is important, too. You need to have plenty in advance of the bad times, as it's likely to be the first thing to disappear from the store shelves when catastrophe hits or even threatens. I try to hold at least a thousand rounds in reserve for any rifle and half that for my defensive pistol. This gives me enough that I can practice a bit or train up another shooter if need be and still gives me enough left that I won't have to fix a bayonet or wield it like a club when the zombies come around. A 4-5 25rd boxes of each of the shotshell types that you plan to use is a good minimum, and a brick of .22 ammo takes of next to no room at all.
I'm not here to tell you that if you have these four guns that you can survive anything anywhere and go on to take down an island of mercenaries like Schwartzenegger did in Commando, but having the right tools and the know-how and willingness to use them will put you far ahead of the curve when bad times come around. But you need to have this all up front, because if you wait until after the hurricane/nuclear attack/second Obama inauguration, you're not likely to find what you want or have the time needed to train up with it. So if you don't have these things, go shopping. And if you do have them, go practice.
So how about it, readers? What are YOUR "favorite four?"