I think pack choice also depends on shooting style and on goal. If my goal is to get to point X and set up a planned landscape photo, any comfortable pack will do as long as I have a way to attach tripod. If I am changing lenses all the time, a think-tank or other belt and lens bags will do, plus any light daypack for the water, food, jacket, and tripod, etc. I rather wish that more packs had Molle-type straps on the hip-belt, these are compatible with most of the velcro-plus-tab lens bags. In cold weather with minimal lens requirements (no superteles or lenses over 3 pounds) a vest will do nicely - there are photo vests, and then there are off-the-rack hunters' vests from Cabela's, Bass Pro, or other big box hunting store. If I am just walking around for a mile or two on easy terrain and stopping frequently to set up, more often than not I just use the default shabby Domke shoulder bag and the tripod in its OEM bag.
One other item: Cotton Carrier vest, for easy carriage and access of camera (or cameras, a second one can be attached to the hip belt). This CC vest works just fine under any backpack. Fine for camera with 400 f/5.6 lens or for 180 f/3.5 lens, with button attached to lens foot - allows use of both hands for hiking poles. Drape plastic bag or shower cap over camera/lens if it rains, or else wear an oversized raincoat and zip it with camera inside.
I confess - I am a tripo-holic and a bag/vest/belt/pack-oholic.