I like my CS spade which I believe was even part of a group deal and now several other members have them. According to a guy who has a real soviet entrenching tool the CS version is better.

While your teacher was in combat knives were an anachronism but now with combat being fought with much smaller units at much closer ranges.
Now knives and bayonets and even in some cases swords (Check out who the AK Ruck
was originally made for)are used both in F.I.S.H style fighting(fighting in someone's house)and bayonets are especially useful for transporting prisoners and keeping civilians at a safe distance.

Also a good knife should be a tool 99 times out of a hundred so it has to have an edge capable of slicing and a point that can dig out splinters without breaking off in hard use. My Sar 5 would make an excellent choice other than the weight is a bit heavy. The YKCG and DMLE or DMDC would make excellent military knives.