I believe you are talking about the Klim krew pac and their Nac Pac. I have both and they are very good pacs. It really comes down to what you want to carry while riding. I personally find that the Krew pac is a little to large and heavy when fully loaded for me to ride with. I have a larger torso and both pacs seem to fit that body type well.
You don't want a pac that is tall if you have a short torso and you don't want to have a short pack if you have a long torso. In either case having the wrong pac will effect how the weight is distributed across your shoulders and back and ultimately cause unwanted strain in both cases. both pacs allow you to carry water, shovel & handle, probe and other essential items such as snacks. they both have padding against your back that provide ventilation between your back and the pac so your back doesn't get too hot while wearing it
Both come with a small tool bag that is securely strapped to the pac and allows you to carry the needed tools to fix things that might otherwise prevent you from getting back to the truck. the tool bag actually comes off so you don't have to carry the added weight on your back. I carry mine on the back of my sled in a tunnel bag. If you carry camera equipment or a lot of supplies i would say the Krew pac would be your best bet but if you just carry a hat extra goggles and snacks i would say the Nac pac would be fine.
