I'm going to suggest that it doesn't matter which rifle you choose, within a fairly large group of good rifles, i.e. M-16, Galil, Sig, HK, Steyer, etc.
If you check your history for the last 150 years, you will find that technology, tactics, gear, fighting spirit, etc, hasn't won many wars, if any. Vietnam included. As an aside, when the U.S. pulled out of Vietnam, our nominal objectives had been achieved. The Viet Cong had been eliminated as a militarily significant or effective force. South Vietnam was lost 3 years later to a conventional invasion from the north with more armor than Hitler used to invade Russia!!
Anyway, back to the point. Since the U.S. Civil War, the side that was able to produce more (guns, ships, planes, tanks, soldiers, etc) won. As an example, we won WWII. German Wehrmacht small unit leadership and tactics were generally superior to all of their opponents, including us Americans. German losses in comparison to Allied losses were far smaller than Russian, American, British, etc. They outfought everyone. Their tanks were generally superior to all others with the exception of the Russian T-34. Our Shermans were nicknamed "zippos" because of how easy they lit up! One Panther was a match for 5 Shermans. But, we produced enough that we could overwhelm the Germans with 10 to 1 or better odds. What won the war for the Allies was production. The Germans (and the Japanese) just couldn't compete with American and Russian industrial production.
In conclusion, pick whatever rifle/SAW/MG combination you want. Some will like it, some won't. But if you can out produce your enemy, you'll probably win.
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Dorsai
Personal weapons are what raised mankind out of the mud, and the rifle is the queen of personal
weapons. The possession of a good rifle, as well as the skill to use it well, truly makes a man the
monarch of all he surveys.
-- Jeff Cooper, The Art of the Rifle