I use a camelbak HAWG for shorter trips, and a gregory z35r for full-day trips.
The HAWG is great for shorter things, but I start to run out of room for the winter and on longer hikes. Also the waist belt doesn't do much for taking weight off of your shoulders, which is not comfortable on a 15-20 mile hike. The Gregory has lots of space and has a decent frame for taking the weight off of your shoulders. My only complaint with it is that it basically has one giant pocket, and not enough smaller pockets. It is too easy to have something get lost on the bottom of the big one.