I tend to consolidate. 5.56MM because that's what I "grew up with" and 9MM because it's universal. I don't think having a bunch of different calibers is a smart choice. If you're an AK kinda guy then go with the 7.62 across the board. If you're a .45 kinda guy then go with that across the board. At the end of the day you want your backup weapons to have the same caliber as your primary weapon. That way you're not fumbling around with different ammunition.