The newer packs used by the military (and there is a wide variety now) carry more and are of higher quality and have the ability to attach more things to the outside. The MOLLE pouches are useful and there are many more types than just ammo pouches. Some of the packs are very large. The external frames are made of a heavy plastic that is less prone to breaking than the old aluminum frames of the ALICE packs. The are a little flexible in sizing.

When out in the remote areas for either work or with the scouts, I like to have certain things attached to the outside of my pack so everyone knows exactly where to find them (first aid, ropes, communications, extra water) without dumping my pack out. This is especially important with smaller packs for shorter trips. I do look for attachment points, even on civilian packs, and have had some civilian packs modified with MOLLE type attachment points. One of the advantages of living near Ft. Bragg is the plethora of parachute riggers who know how to sew on heavy nylon. Some of the gear companies actually started around here with former riggers modifying gear for soldiers (and we used to get in trouble for having our gear modified, now it is normal, even expected).

One advantage to military surplus gear is price and availability. Here it is coming out of our ears and the prices are very reasonable. It is better to have a pack that works than to not have a perfect one.

I am with Hikermor though in that I prefer to have a higher quality and better design than you usually find in military gear. For my scouts I steer them towards surplus just because it is more affordable. Many families have financial difficulty and this removes the obstacles that prevent the kids from participating. It can also ensure that they have what they need and that it will work. Especially when you are talking winter outings. Long underwear, boots, jackets, ponchos, sleeping bags can all be very expensive. The military stuff will work and keep them safe. It is hard to find smaller sizes however, for the younger scouts.

There are some newer civilian brands that are improving in quality, but they are also going up in price. Outdoor Research (OR), Alps Mountaineering, High Sierra have all improved in quality and are much more affordable than Mystery Ranch.

All of that being said, if you feel that you need to evade notice and sneak around the brush, by all means get a military pack. They work. A bright color is safer though. Zombies don't care what color you are using!