I like osprey packs, they fit me well and are light, well thought out, and the warranty is forever. I don't have to carry out a deer, so take that into consideration. They are also fairly spendy.
You really need two packs, unless you are willing to carry a large pack that is nearly empty while day packing. If you want a cheap back, the ILBE packs are supposed to be good (designed by Arcteryx I believe) and cheap. I have thought about buying one as a loaner/spare but I never got around to it.
I just broke down and bought an osprey day pack after using various cheaper daypacks. I haven't had the chance to use it, but I am looking forward to it after using 'book bag' type packs for years.
