I am attempting the AT next year with one other person and I decided to go with my old boy scout roots and stick with an external frame backpack. Since my previous one was made for a 16 year old doing weekend hikes I will be upgrading. I want to stick with kelty because even though I'm not going to use my old pack, it's still very useable and durable. I found and old kelty at a used gear store for $50 and will buy that one unless someone wants to suggest a different brand.
Fetter