You know - I have bought and used a few different packs - Gregory (Shasta I think?), Dana Design Astralplane, Osprey Aether 60 and 70.
I thought each of them were comfortable, and spent a decent amount of $$$ on each of them (except the Astralplane - that was actually a freebie!).
However - last year I sold all of them on ebay, and spent a little more money to get what I consider to be THE pack. I got a McHale Popcan:http://www.mchalepacks.com/ultralight/detail/summit_pack.htm
It was definitely expensive, but I will never part with it because it is by far the most comfortable pack I have ever used. Even better than the Astralplane - and that was a really comfortable (but heavy!) pack. I can pack the McHale pack sloppy, pack it neatly, pack it overfull, it just doesn't seem to matter. It feels great no matter what.
The one I bought weighs in a bit over 4lbs and I had it made to carry 4500cu in.
It is the best money I've spent on a piece of gear.