Problem is, weaponry is a toolbox; You have your hammers, your screwdrivers, your crescent wrenches. You don't turn a screw with a hammer, or drive a nail with a crescent wrench. No single gun does everything well.
If I had to choose ONE gun to last me for the foreseeable future, given my current set of circumstances, I'd have to go with my Sig Sauer P226. I don't hunt, nor do I plan to have to hunt. And if the SHTF, hunting game still isn't on my list of likely necessities. Similarly, long range work is neither my forte, nor what I imagine will be necessitated by such a scenario, being that I live in an urban area.
Defending myself from incidental close-quarters violence perpetrated by my fellow man is much more likely. Having a weapon that escapes immediate detection is also going to be useful, because in such a scenario, folks moving around with long guns are going to attract the attention of whatever remnants of authority still exist. My nightmare SHTF scenario involves the duality of a governmental crackdown on the nominally law-abiding, coupled with a near-total absence of meaningful law enforcement aimed at regular crime. In other words, I'm afraid of the government being more afraid of me (i.e, citizens in general) than of the criminals, or no longer bothering to distinguish between them. Thusly, my toolbox has to consist of a weapon that is both effective at close-range combat with lightly armed, unarmored targets, and is capable (with luck) of escaping detection in cursory examination by targets I am incapable of engaging either by dint of authority, numbers, or weaponry.
I have a good chance of being able to do whatever needs doing in the short term with a Sig P226 in 9mm, until I can meet up with some friends of mine with different skillsets and more varied weapons. As implied by the post, my entire plan in just about any SHTF event involves a bug-out, as my current residence is not a defensible position, and is rather likely to be "behind enemy lines", whoever the "enemy" happens to be. Safety is not here; I have to escape to it.
