I think it was pretty much US manufacturing and Russian bodies. And that was with the US and Brits simultaneously fighting the Japanese. OTOH, my uncles were in the European theater and did credit the Germans as the best soldiers (not sure, maybe they meant the best soldiers of the Axis).
Most military historians will concede that man for man they were the best soldiers of the war. The training regimen was as you might expect from the Nazis, ruthless and brutal, but very effective in hardening and toughening up the soldiers before they reached the front. “Through Hell for Hitler” by Henry Mettalmann is the memoirs of an ordinary German landser and is an interesting insight.