All thoughts, experiences, abuse.......relatively welcomed
as it happens i'm pretty deep into more or less the same process as it sounds like you're into. i tend to go mil-surp because i like solid gear and don't have bags of cash to spend.
big question: what size bag do you think you need? 40L? 60L? 80L? bigger?
for the smaller end of the scale i'd personally go for something that has "cargo capabilites" as they say. in other words some way to expand your carrying capacity, usually with zip-on or MOLLE side bags. so something like these:
British Desert DPM Field Pack 45L or British MTP Infantry Pack 45L (basically same bag, different camo)
British Desert DPM Bowman or 60mm Mortar bags (as above but with waist belts plus a big of weight due to unusual secondary compartments).
Snugpak Rocket (60L?)
DD Bergen (55L?) (a somewhat lighter duty bag)
Karrimor Predator 45L (££)
Wisport Racoon 45L
(there are heaps of "military style" bags of this sort but far too many are a bit feeble in execution, caveat emptor)
for 80-100L bags i'd very much recommend looking at the British and Dutch DPM bergens: damn well made and good prices if you shop around. The British comes in long or short back, the Dutch bag has the torso adjustment (move the shoulder straps up or down). there's also the old Belgian 80L bag -- very similar to the Dutch in design -- but most folks gag at the "Jigsaw" camo pattern, cheap as chips though. all of these accomodate zip-on rocket pockets though the Belgian zippers go the "wrong" way round.
for bigger bags i can't say much as i have no applicable experience.
i should add a few words about the camo on mil-surp bags: don't forget that dyeing is always an option. for instance i've had pretty good success dyeing British Desert DPM to a darkish green or brown thus making a completely unappealing looking bag totally acceptable. cost of bag + packet of dye + an hour or so of your time = good kit at very reasonable price. just saying it's an option if you are so inclined.