Man this one has been going a while...
Of the guns I own or have access to:
1. I am a rifleman. And the M1A/M14 is a "rifleman's rifle." I'll take my M1A Loaded. It already has the ARMs mount. I was holding out for a decent DMR optic, which as of now on this market doesn't exist, but if forced to choose I'd put something like a 1.5-5 Leupold MR/T on it. A little long for inside stuff, and heavy, but decent balance, and I won't be fighting inside. In the hills, the range, power, and penetration of an accurate, reliable semi-auto 7.62x51 like the M1A is worth the added weight. This rifle can be used for everything from range and competition to hunting and defense, and parts and ammunition are available domestically enough to be able to find it easily when the revolution starts...which if I can only have three guns is going to be here directly.
2. My Ruger 10/22 with Weaver 2.5-7 rimfire optic on it. Lightweight and portable, ammo and parts are everywhere. Good for small game and plinking, and if necessary, close range defense. I've tried it out on some drills and I think both eyes open on 2.5x, mag dropping on the head could be effective. No recoil, very accurate and fast follow ups, and it wouldn't really take 10 hits to put someone down. I'd just engage the head until the threat went away and fight my way to the M1A, or whatever else is available.
3. SIG P220SAO .45 ACP. I'd actually prefer my G20 or just about any other Glock but don't have access to them and fear 10mm ammo could be hard to find. The .45 is available here and the SIG works well. Little more complex and hard to find parts for than I would like, but it is pretty reliable, accurate, and thin enough to conceal. Good close in fire for defense.