OK I like Military Rucksacks...
at present I have the largest selection I've ever owened:
ALICE large pack
Alice Medium sack (fits the same ALICE frame above)
SAS/PARA rucksack with frame/straps
58" Large pack (lol)
OG PLCE bergen
a PLCE bergen I've modified to be more user friendly.
and a A snugpak Rocket (not really military but similar features).
Nothing has ever gone wrong on any of them, I usually have carried far too much, and I tend to walk fast rather than plod along.
OK just for starters It's My own opinion, after using each of these over the last 20 odd years:
for short walks nothing adventurous perhaps in and out of towns I'd opt for
ALICE Medium with frame, it's about 30ish litres but sturdy enough if you want to carry something heavy.
PLCE sidepouches if not carrying lumpy things.
or Snugpak rocket, which I'm always worried about breaking!
for long hikes (comfort and reliability are priority)
ALICE medium or PLCE without side pouches as they are more supportive and more comfortable generally (yes I know they are basic and lack modern technology)
for short hikes with overnight camp (capacity is priority)
ALICE with Large sack, SAS/Para Bergen, or PLCE with side pouches.
If travelling to a base/camp then setting off from the base for day trips
I would always opt for the PLCE as it is far more adaptable than the other options easily adapted for climbing/hiking/kit carrying.
Strengest I would say PLCE and SAS bergen are best.
Weakest/Prone to damage I would say is the Snugpack followed at a distance by ALICE sacks)though I've never damaged one the fabric is softer than British sacks (the frames are pretty tough though).
ALICE and SAS/Para both have many exposed straps over the external frames which does cause wear but the advantage is you can see the wear before it breaks, and when it does it's easier to repair unlike PLCE/SAS or modern climbing sacks.
lightest: PLCE Sidepouches, Snugpack, then ALICE medium without the frame
Heaviest: by far the SAS/Para is the heviest it has a steel frame. it's also the least comfortable and has little padding and has no waist strap(but it's how it's designed).
least comfortable 58" large pack with no padding or frame at all, even when worn with webbing and packed carefully (as it's designed) it is a back ache waiting to happen!
Weather resistance: SAS/Para would have been the best, but the fabric is worn PLCE is the next best, ALICE has very poor waterproof fabric.
overall I would choose the OG PLCE bergen purely as i'ts tough, less to go wrong than the others, resonably comfortable, resonably weather resistant and with the side pouches and compression straps it's easily adaptable to changing activities.
I summerise my bags like this:
for hot weather or laid back activities I'd use ALICE as it has better ventilation and usfull storage pockets.
for cold weather or anything serious like scrambling or 2 or more days expedition I'd use PLCE.
I only really carry the SAS/Para Rucksack when empty to try to loose a few pounds when walking the dog!
None of them have a good supportive waist belt not even the Snugpack! as they are all designed to sit on top of webbing pouches!
None of them have sternum(chest) straps
Yes, I know Army rucksacks are cheap/heavy/badly made etc and that there are more comfortable rucksacks, I used to work in a camping shopIt's only my opinion!
FYI on a recent family walks in wales I used a Civilian Deuter 50l rucksack that had floating adjustable straps all the bells and whistles etc. it had a supportive belt and everything else you'd expect frm a modern sack...but I prefer Military sacks for everything else.