Mudjunky,
Your question is a difficult one, more so then you might think. Although you have come to a knife forum to ask a reasonable question expecting feedback from those "in the know" the truth is most knife enthusiasts have personal preferences, biases, and are hardcore fans of one brand or another, plus different personal experiences.
As mentioned the responses will differ greatly and cover a wide range of different brands and types of knives and be as varied as the opinions of the people here and not necessarily represent the "best" as there is no real "best" but rather personal opinions and favorites based on individual experience and beliefs.
Some may have actually served in the military and deployed and some may have not. And of those that have their experiences will be just as varied and reflect what they used their knife for during time in service.
Ranging from using their knife every day all day to hardly ever and maybe just to open a can. A sailor would have used his knife very differently then an Infantryman. Someone in supply might have used his knife non stop all day while the guy on patrol never used it once or not often, or maybe he did. I hope you see my point.
With that being said, the top production knife makers like Benchmade, ZT, Kershaw, Spyderco, Hogue, and even Cold Steel and some others I forgot to mention all make some very good, strong, dependable knives. They all make what they consider hard users and have several of each in their line up.
A good knife from any of these brands in the price range you put forth will be good enough suit most purposes.
Take some of the suggestions made, look them up and if they look strong and tough to you and are from the companies above, they probably are.
Also, during my 20+ years in service I used my multitool, both Leatherman and Gerber far more then I ever did my knife, however, as useful as it was it never replaced my knife when a knife is what I needed. If possible it's great to have both.
Best of luck and all the best to your friend.