Since I started this post going on 10 months ago, I have done a great deal of hiking with packs and pack comparing. I, like some of the posters, have realized that it makes a lot of sense to separate packs for hiking and similar tasks from packs made for more "military" type purposes, meaning carrying a lot of weight and bulky, heavy items and still being able to take a great deal of abuse over a long period of time.
My first pack was an eberlestock X2, which is a smaller bulletproof military style pack. I like it, and it has a great suspension and is most certainly bulletproof. But the fact is that I don't need that (and don't want to lug around the weight that comes with all of that) when I am just going for a day hike. So, after a lot of consideration and trying on packs, I picked up a Gregory Z30, which I load with probably 20-30 lbs. when I go on day hikes. I also liked the Osprey stratos 26 ... the deuter futura 32 also looked good (and they can be had for low prices) but it is kind of heavy. All three of these are ventilated packs, which I decided was a feature that I wouldn't go without.
I plan to do a comparison post of the eberlestock and the gregory. Long story short, the gregory is lighter and better for carrying only what you need for a day hike. It is built well, but certainly not bulletproof like the eberlestock. The eberlestock is much better for organizing your gear (it would be much easier to live out of (as opposed to just getting gear from point A to point B) than the gregory), and is much more versatile in terms of allowing you to stowe bulky items (e.g., if you are loading up half of a quartered sheep or something) and carry a lot of weight.
I took this logic to my big packs too -- I have one tough military style pack (a Kelty Falcon 66) for a bug-out-bag and applications where toughness and/or versatility are more important than just being able to get necessary gear from point A to point B. For my high performance hiking pack, I settled on an Osprey Atmos 65 ... I thought that its ventilation system was the best out there, and it fit my body much better than any other pack that I tried. It also is closest to what I wanted in design -- a good suspension system (i.e., NOT an ultralight rucksack), but still made to be light weight. I haven't given that pack any work yet, but I expect good things from it.
I may look to replace the kelty with something like one of the lighter eberlstock hiking-style packs or maybe research some other packs (like dana designs packs) that are built very tough and able to carry heavier loads very well. I think my kelty is pretty tough, but I can tell that there are tougher options out there. I probably won't ever want to spend the sort of money you need to for kifaru or military-style mystery ranch packs.