I have the Brenthaven backpack - best back I've ever owned - period. I've had a ton of messgener bags, backpacks, etc. and the Brenhaven is the best. It comes with a removable sleeve - well padded. It's guaranteed for life, has TONS of pockets and is very comfortable to wear. I had a Waterfield Cargo bag (large) that was excellent - my problem with that was not the quality of the bag it was that for hiking long distances a messenger type bag sucks. The Brenthaven is awesome - I can load it up with tons of stuff and it never really feels bad on the shoulders or back.
You may want to look in the PB forum at Macnn.com - they have a sticky forum in there dedicated to bags.