There are some great suggestions posted above, however, I would add my advice and hope it will help.
Try to talk to people (for example here on the Forum) who have tried many models and brands and ask specific questions to finalize your decision. I am by no mean an expert but might help you to narrow down your research.
It is worth to think/go over the following:
- USE: For what (trail hiking, bushwacking, canyonering, winter hiking, mountainering, expedition) and how often would you like to MAINLY use it? How long would you like to MAINLY live from your pack (dayhikes, weekend getaways, weeklongs, crosscontinent)? That is going to narrow it down regarding size (from-to), weight, construction (external vs. internal, waterproofing).
- PRICE: Set up a reasonable price range (from-to) for the desired use determined above.
- TRY-ON: Go to some close-by dealers and PUT it ON with the expected full weight (they gonna help you with that) and mingle around in the store to get a feeling about it and to CHECK its COMFORT for your body shape. That is probably the most important thing IMO. However, I still yet to see a dealer that stocks the many brands and models that are on the market so a compromise is inevitable.
- Think it all over and go for the best one you can afford or happy with.
Few other points:
- Use Backpacker magazine, especially March 2001 Gear Guide issue to see the full scale of options and some recommendations. Use
www.gearfinder.com search engine too for a start.
- Some (especially on this Forum) like military and combat style backpacks like Becker Patrol. Try to check earlier posts for those if interested.
- Weight matters and I prefer the simplicity of toploaders (vs. panelloaders) with a top and slim back pocket instead of six large pockets all over that are limited in size.
- Adjustability and versatility are good but too many bells and whistles are not.
- I prefer a slick medium size internal frame that hugs my body over an external frame or any monster pack. It is also easier to move with in denser vegetation or on slippery surface.
- I would stay away from frameless things.
- I am still not a big fan of hydration systems and prefer two side mesh pocket for water bottles.
- I have a Kelty Hurricane 4900 cu. Inch.
Hope it helps,
HM