There's a lot to consider when buying a pack. The most important is FIT, period. This involves torso length (from the C7 vertebrate to the illiac crest (top of hip bone)) being measured along with your shoulder width. For an optimum fit it's also good to understand the curvature of your back, especially with packs that have aluminum stays (which can be bent). The next consideration is SIZE. How big do you want your pack to be. A couple of things to consider; too small a pack will limit you on the length of your trip. However, too big a pack with allow you to carry too much stuff and the pack itself is much heavier. It's important to note that bigger packs (4000-6000 cu in) can be used to carry smaller loads, but small packs (2000-4000 cu in) cannot be made bigger. Personally I think a 5000ish cu.in. pack is just right for someone who wants a pack that will go a week, but can also be used for weekend trips. The next consideration is WEIGHT of the pack. There are many options available today, but if you want one that's super durable, the pack will be heavier. If you're tough on gear, I would recommend one that doesn't contain much sil-nylon material, especially on the outside. The Denali Pro is a great pack for expedition use, but it's probably an overkill for most recreational backpackers. A better option would be the Gregory Whitney or Palisade. Osprey makes some great packs (the Argon is highly recommended) as does Granite Gear. If durability is what you want, Granite Gear's Stratus 5500 won the "World's Toughest Pack" competition put on by Backpacker Magazine a few years ago (they dragged it behind a jeep going 65mph on a dirt road with 25lbs of weight in the pack). Granite Gear packs also don't include stays, but have composite frame sheets that work very well in comforming to your back. I've owned a few over the years and have had great experiences. Arc Teryx also makes great packs and was recognized as the "World's Toughest Pack" along with Granite Gear (the standout being Bora 80). The last thing to consider is that your backpack is the most important piece of gear you will buy. Make sure you take the time and make the effort to find exactly what your looking for.