I have whatever the heck Jam they sold circa five years ago, and it fits me so is a nice option. In summer. I'm simply not disclipined enough to use it for winter backpacking, as the capacity isn't there, plus the upper weight is roughly 20-25 pounds.

For winter I'd want more capacity (60L or so) and some kind of frame--probably a hoop.

cheers,
_________________________
--Rick