In reply to farmer:
Echo the comments about fit is everything. The world's best pack is as much use as a chocolate teapot if it doesn't fit you. However a cheap pack may be perfect. Each manufacturer sets their packs up slightly differently.
Go somewhere like Go Outdoors, and spend a reasonable amount of time trying things on - they usually have weights there specifically for weighting packs when trying on.
We spent a couple of hours getting Lady Blue a pack recently, and after trying a number on, none of them quite worked or sat right regardless of how we messed with the adjustments. Then we tried another and it fitted perfectly. Wasn't the most expensive or the best or biggest, but it was the right one.
It's not like we had a budget either. Basically the idea was "best fit, money no object" (Though if it had gone over £300 I might have winced). Ended up spending £95.