I'd think any backpack would be a vast improvement over a duffle. If you state your specific requirements you'll likely get specific recommedations. How much weight are you planning on carrying? Are you just backpacking or hunting and will need to pack out game? How much is breaking the bank? Without knowing this it's hard to reccommend specific packs. That being said USMC IBLE is cheap enough, rugged, and far supperior to a duffle. I'm a fan of the old Dana Design packs can be had on online auctions.
