Ok heres my modest opinion...
I spent alot of time working in ski and outdoor shops in the winter so I have owned and used more packs than I know what to do with! I own packs from...
Lowe Alpine, Marrmot, Mountainsmith, Gregory, old Dana Designs, Camelback, and a few others, in a range of sizes and styles.
Having said that the best day pack I own is... one a smokejumper buddy of mine stiches up for me. It is the pack they jump with. Great in the woods, carries the weight low on the hips, moves with you, an alows me to carry a slung rifle. I carried these packs for 10 years in the BLM fighting forrest fires, it is also my hunting pack GREATEST design going IMHO. I have never seen anything like them from the large commerial makers. It is designed to be carried like a huge fanny pack, not up high on your shoulders. It was designed by the men who use it, and it WORKS!
Hoggans packs makes as close a copy as I can find, and, having used this pack, it is a pretty nice.
http://www.hoggans.com/rescue.html
Hot Shot Ruck 154 model is close but not as nice as the one I have from the Jumpers. I have to say i have hiked more miles than most, in all sorts of terrain and these are great day packs and comfortable up to 50# my usual load working fire was 35-50# sometines more if I was running saw. For those of you who can't live with out the silly thing you can fit one of those hydration bladders in it. There is a pocket against your back (made for the shoulder straps to tuck into when they jump) one of the smaller bladders fits in it. The outer pockets will carry 2 nalegene bottles each, and you can reach them while walking. To top all of it off it will fit in overhead bins when flying. I love this pack!
Mark