The “best” isn’t the one with the best ballistics. It’s the one you’ll be able to maintain a supply of long term through barter or stealing.
Look for the most common, not the best shooting.
That is right. If a SHTF were to happen you want a caliber that is the most common. 308/5.56 are military rounds and are popular which means there is ALOT of it out there. There is probably Trillions of rounds out there. Also 22 long rifle is the most common round out there.
12 gauge supplied with 7 1/2 shot and slugs.
.30-06, .223.
Seems common enough.