You will probably find much better comfort and adjustability in a civilian backpack. A military pack might be more durable. Maybe.

My favorite pack is my Deuter. At the time I bought it, the mesh back panel was really innovative. Now-a-days, I'm sure other brands have probably copied it by now. The mesh makes the pack so comfortable and cool to wear. These pictures are day packs, but Deuter also uses this mesh system on larger packs.