I'm with OM. Brand doesn't matter. It is how it fits you and your gear that matter. With a high quality brand it may last longer... but it will last a real long time if it sits in your closet because it is uncomfortable.

In terms of doodads and options, I think less is better. They all add weight which make the pack heavier on your shoulders. Even waterproofness. I just shove my quilt and clothes in a garbage bag. It ends up being lighter (or similar weight) to buying a waterproof backpack. Unlike a waterproof backpack, when I get a hole in it I just grab another one.