Grannyknot asks some very good questions. Having recently been through a similar effort you need to ask yourself quite a few questions before making a purchase.
Below is a link that is useful for helping those narrow down what category of packs they should purchase:
Finally, regardless of what everybody tells you, the best thing is to go to a store and try on as many packs in the range you are looking at as possible. Then determine which one offers the balance of size, comfort, features, and cost that you are looking for.
Personally, I recently bought myself a Gregory Z65 because it has the volume I wanted for overnight winter trips, 3+ day summer trips, reasonably light weight for a 65L pack, comfortable, and it was on clearance since it was a 2011 color (lots of deals to be had on 2011 models). That being said, it is hard to go wrong with any of the main pack manufacturers: Osprey (just ordered a Stratos 24 from a local store), Gregory, Deuter, & Arc'teryx. I did purchase a High Sierra prior to the Z65 but it was such poor quality and heavy I immediately returned it in favor of the Z65.
Good luck, and enjoy your trip.