3:39 p.m. on March 11, 2012 (EDT)
this reminds me of a t-shirt a friend gave me - 'why your backpack is better than a girlfriend.' fortunately, it's a size too small, because my wife doesn't appreciate the humor.
a number of quality brands make packs designed for women: arc'teryx, gregory, osprey, golite, black diamond, granite gear. Mountain Hardwear, REI, & Deuter as well, but i don't know those well enough to comment. err on the high side in terms of volume and carrying capacity if you hike with kids. the best way to figure that out is to gather your gear, fill your 40 liter pack, empty it, then put in all the stuff that didn't initially fit. i'm roughly guessing you might have to size up to about 65 liter, though. (i'm assuming most normal people will not bring their gear to the store to do this).
take the advice above that you should go for fit and comfort above all. that means trying them on, carrying roughly the amount of weight you expect to carry. any decent store will have bags of sand and other filling to simulate carrying your stuff. it takes a while to do this at a store during busy shopping times....but it is definitely worth the effort to get it right.
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one person's opinionated impressions of the brands, from a combination of trying things on and walking around with them a lot. any one of these brands make backpacks that you could use regularly for years and will have a pretty good set of features. pockets and such are definitely a factor in getting a backpack you like, but that should be secondary to how they fit and carry.
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Granite Gear and Golite tend to be lighter weight, though Golite's larger backpacks (eg the Terrono) are pretty average weight-wise. (granite gear makes 60 liter backpacks that are under 3 pounds and can comfortably carry a decent load).
Gregory and Osprey tend to cover both the lighter (but not ultralight) side, but also offer a line of heavier, burlier backpacks capable of carrying more and suffering more wear and tear (the Osprey Aura line is about a pound lighter, on average, than the ariel line; the Gregory Deva line is about a pound and a half heavier than a similar volume backpack from the Jade line).
black diamond's DNA comes from alpine climbing; their backpacks tend to be oriented toward that kind of usage, somewhat. they tend to be on the heavier side, weight-wise, because they anticipate some of the abuse you get from climbing.
arcteryx tends toward the heavier side of things - even their attempts at 'lighter' backpacks are still pretty heavy-duty. on the plus side, though, they carry a lot of weight easily and are made of pretty robust materials, so they tend to last a long time.
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i didn't mention mystery ranch as an option because i don't think they make backpacks specifically for women; trying them on would mean ordering one and having to return it if it doesn't fit, because they sell direct from their business in Montana; and because they are on the expensive side - on par with arcteryx price-wise. But, their backpacks have been uniformly outstanding for me. their standard backpacks are quite heavy; they make one on the lighter side, the Trance XXX, that might deserve some attention if you hike a lot and if it fits. (would help to know if any women use and like mystery ranch.....)
happy hunting!