In my experience and opinion, how the pack carries the weight is far more important than how many pockets or cool compartments.

I've had bigger packs that have carried much more comfortably than smaller one. The key for me is a good, wide waist strap and a solid back to the pack. It keeps the weight higher up on your back and not sliding down toward your tail.

Backpacks are key for where we hunt. ATVs are not allowed so we hike several miles back in every morning and evening. Having a good backpack makes a big difference.