I’ve heard a lot of thru-hikers are using Osprey’s these days but I have no experience with these backpacks. In my day (1994), the Dana Design Terraplane was all the rage. I upgraded to a medium Terraplane in Hanover, NH (5800 cubic inches) but it was too small for me in size (not in capacity) and I eventually bought a large Terraplane (~6200 cubic inches) in 1996. I use the large Terraplane on short backpacking trips to this day. The only issue is that the Terraplane is really heavy – 7+ lbs.
With all the advances in technology since ’94, I’d shoot for a pack that weighs no more than 4 lbs. My “go to”