I've spent a lot of time trying to find the right camera pack for me. The short answer is there isn't really a perfect, one-size-fits-all-scenarios solution. I used a Think Tank Photo for a while, an Osprey pack for a while, but have landed on the f-stop Gear Tilopa as my outdoor / adventure photography workhorse.
The video below is my review of the Tilopa. This is a 50 liter pack that is built with an internal metal frame like a normal backpacking pack to help carry heavier loads. Their internal camera unit (ICU) system allows for customizable internal configurations, and overall, the design and engineering is top notch.
In this video I go over why I chose it, and my experience with it so far. Post questions to the comments (here or on YouTube).