I've always used pack frames for packing meat and my preference was solidified a couple of years ago. Carried a mule deer 6 miles in an Eberlestock before stashing it in a tree. Came back in the morning with a Kelty external frame pack to finish the job (3 more miles). I really, really, really prefer the external frame!
With that said, I'm not about to carry a frame pack while hunting and I like being able to carry out the first load on my way out to get a frame. Haven't found the right pack yet, though. My Eberlestock is unnecessarily heavy. Don't like the fabric of my Badlands pack (loud and stiff in cold weather) and I don't think it will survive more than 1 or 2 heavy loads. Don't relish the idea of spending even more than I spent on the packs I have. I'm starting to think a mountaineering pack with a lightweight homemade cover might be the way to go.