This is my first post here and let me say thank-you in advance for this opportunity. Now as far as a hand held combat weapon, I cannot say. I have always felt that the only true way to judge a weapons combat worthiness is to do combat with said weapon. The fact that I have not personally been in that situation with those weapons I cannot say which is the best. I have had the opportunity to fire some rounds from a variety of weapons from that era and can pass on what I found evident of the weapons some 50 years post service.
My personal favorite was the BAR or Browning Automatic Rifle. I found that for all its cumbersome downfalls, the rifle I fired was both reliable and repeatable. This may or may not be the case for the majority. I also like the stopping power of the 30-06 round especially compared to the prevalent more modern .223 round. The Russian rifle/sub guns from the era that I’ve had contact with were terribly inaccurate. Once again this may or may not be the norm. I also love the 8mm Mauser bolt action for accuracy, very repeatable patterns, but this was not breaking edge technology in 39, it pre-dates the conflict.
As far as the greatest weapon of WWII, I find myself impelled to write that, in my opinion, that the nuclear bomb was the greatest jump forward that warfare has ever seen. (It is arguable that the introduction of the firearm into warfare was the greatest, but the initial result was not near as effective.) And the introduction of the nuclear technology in warfare has saved more lives since 1945 than any technology. The threat has weighed heavy on the minds of every human conscious of the ability to phathom the true threat that the “nuke” holds, yet it held the west and east at bay from full war for 50 years. No nuclear power every dared engage in “total war”. That is because total war meant the possible/probable? end to life as we know it. The Korean or Indochina conflicts surely would have been escalated to enormous scale if not for the fear/knowledge that no one wins, if no one survives. In almost a Dr. Strangelove way nuclear weaponry kept the “big Dogs” from fighting with just the shear magnitude of the outcome.
From the Trinity tests to right now no WWII era weapon has made near the impact as the 2 bombs that changed the world. There were effective weapons, this include all the handheld weapons mentioned previously in the thread. There were tactical advances; this includes blitzkrieg and mass arial bombardment. There were technological advances such as the V2 and the jet. I still nuclear technology was a leap forward. There weren’t thousands dropped, only 2. Those 2 changed the course of history.

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The meek shall not inherit the earth, if kept beneath the heel of the jackboot.