I also like external frame because they breathe the best. Some of my wishes:
1. keep it under 2lbs total
2. mesh side pockets all around to hold 2L bottles
3. Total waterproof material
4. no zippers (helps w/ #3 above)
5. I like top loaders
6. shelf to strap outside items
7. not critical but nice: variable torso
8. if not <$150, Iíll just stay with internal/no frame packs.