The most important characteristic of any pack is that is fits and is comfortable for the user. You need to try it on in the store, loaded, and walk around with it a bit. If the store can't accommodate you, walk away and try somewhere else. If possible, borrow or rent one and take it on a trip.

Everybody and his brother makes good packs in the size range you are contemplating. Not surprising, because they all come out of about three factories in the same industrial district in China nowadays. Some brands I have enjoyed are REI, Arc'teryx, Mountainsmith, LL Bean, and Kelty.