Like Biatholonman, I've had a lot of exposure to various backpacks. I spend a fair amount of time living out of one.
Kifaru is likely the best player in the backpack hunting game. It's what I use most of the time. They're expensive, but they're lightyears better than anything else in that price range. Tax time will see me ordering a Bikini Duplex, with a 7000" bag, and something 5000"ish. Then I'll be using Kifaru for ALL my hunting (and fly fishing, scouting, and backpacking)
My advice, try all the packs you can, especially with loads over 65 Lbs if you're planning on packing meat. Buy the one that sucks least.