Both are good, but I rarely use my Runners KB after getting the Original. It's got more room but if you don't stuff it it's not really bulky. And I've found that I can actually draw about as fast from the KB as I can from IWB (faster if I'm wearing a T-shirt over the gun).

They also sell pack lifters used to integrate it onto a backpack. I've never tried them but reportedly they work well. I've found the KB to work and play well with a regular backpack.

I think the Original KB is the way to go if you plan to use it as a pack without a firearm. You can fit more in it for sure. But both are good. At one point I thought I might add a Snubbie to the mix but really there's no good reason to since the larger ones are very comfortable. But if they ever do another run in Black I'll be getting one.