Oprey Argon or Aether? Arc'Teryx Altra?

Well the real difference is the weight. The Aether is a stripped down lightweight version of the Argon. It will have a lighter suspension system, less features, and possibly a lighter material. It is about 1.5 lbs lighter if I remember correctly, which is significant, but you will sacrifice on features and comfort. Either way, 75-85 L is a big bag. Dont get me wrong, I own the Aether 85, but trust me, it is big. Way too big for solo hiking. Most solo trips, except dead cold winter ones, should only require 50L or less. I have only used the 85L bag for multi-day mountaineering trips. It is probably best to get mulitple bags, and if you think you will be doing the hiking first and foremost, I would get that type of bag first. As far as the Arcteryx bag goes, Im not familiar with it, but their gear, while expensive, is very high quality. I don't think they would make "gimmicky" gear. The downside with their gear, especially packs, is that they are inexcusably heavy (usually).