I'll comment.
First, what does SHTF mean? This hasn't been clearly defined in this thread.
Are we talking about a regional/localized natural disaster with the possibility of a protracted disruption of services and supply chains?
Are we talking about some kind of Red Dawn situatation?
Are we talking about a post-apocalyptic, zombie-infested world where we all run around with spiked shoulder-pad and painting our faces?
What you are envisioning is fundamental to the question.
What firearm to take? Where are you going? What resources do you anticipate there and how do you think you'll procure them?
Me? I'm not going anywhere. When people talk about "bugging out," they usually are talking about heading to somewhere like where I live.
Because there is very little that can occur that will uproot me, the issues of caliber becomes moot. Stack deep, and you can feed what you have.
For that reason, I'll take what is best for the job. With me, it is different calibers. I'll take a rifle that has more power/ magazine capacity than my handgun. For my handgun, I'll want something that I can conceal easier-- that typically means a semi-auto. I'd also want the abilty for faster follow-up shots. That also means a semi-auto.
If we are talking about a Katrina-like situation, you aren't going hunting for your food. It isn't the same as a post-apocalyptic world. You want a handgun above anything else. I've posted about this several times on THR about my experiences in Katrina.
If you have to go into public (and you will at some point) you can't carry that shotgun, AK, or AR without getting unwanted attention. When doing the hundreds of chores that you WILL have to do to get life back to normal, you can't have a long gun stapped over your back. If you leave the long gun in a vehicle, or laying near you while you work, it is useless to you if you need it. And it is out of your supervision. If you have kids or other people around, you may want to consider that.
You want a weapon that you can holster and still work or move about with little attention.
If you have to go to a shelter, do you really think they AREN'T going to confiscate a long gun?
In Katrina, I kept an AK in my jeep or by my bed when we slept. For 95% of the time I was outside, it was impractical to keep up with. It stayed in my Jeep. Practically ALL of the time, I kept a Glock 19 with me.
If we are talking about a "Red Dawn"-like situation, it would be in your best interest to have your firearms the same design and caliber as the military units you will likely be encountering.
The reality of some SHTF scenerios is very different from what many people envision them to be.
If I were in a post-apocalyptic world, it would probably be best to make sure one of your firearms is a flintlock. I don't see any more ammo shipments coming to Wal-Mart in that world.
-- John