Upload & Sell: On
I have tried a great many backpacks and have settled on a set of two - the TTP Streetwalker HardDrive and the F-Stop Loka. I also have an F-Stop Tilopa that comes out for big trips but is otherwise too large for general use.
The TTP bag is my daily haul as it carries my laptop nicely, mates to the Speed belt and accessories nicely (for urban, event use) and stands up to a lot of abuse. The Loka, as Steve mentions, is lighter and doesn't hold quite as much as the TTP pack, but is perfect for field work, short hikes (2-8 hours) as it carries water nicely, and as storage.
Generally my core gear is divided between the two packs and both are with me or handy at all times, all I need to do is swap body and a lens or two and I'm ready to use whch ever bag fits the moment. That said, if I had to choose one it would be the TTP, but only because of the laptop storage. If I was choosing one and did not have to carry a laptop the Loka would win out.