I love the clamshell-style backpacks. There is a small daypack I use sometimes and I inevitably wish it was the clamshell/front-load/panel-load style. So much easier to get to things without unpacking everything. I recently ordered the ULA Dragonfly and am anxiously waiting to receive it; the clamshell opening with an undivided, deeper main compartment was one of the reasons I chose it. With that said, I think packing cubes are helpful with an undivided packing space.