I've always stuck to common and nato varieties because of availability. 5.56, 7.62 x 39 and 51, 9mm, 40, 45, and 12 guage. In the event of a natural catastrophe and you find yourself scavenging, you can usually find it in the wild (citizens, law enforcement, or military.) Guys I know with uncommon ammo also reload and can fall back on that in time of shortages. I do have a couple of oddballs though, but my everyday stuff is common.