If I remember correctly this study (called "Fighting Power") by Israeli historian
Martin van Crefeld, he concludes that compared to the US Army the German wehrmacht at the time was more effective especially due its objective focused command structure, called "Auftragstaktik" (as has been mentioned before in this thread). This was in contrast to a stiff and bureaucratical style of leadership on the US side.
Another issue that is being raised, is the duration of the training the soldiers received. In case of the Germans the training began essentially at childs age during Hitlerjugend and earlier with games deliberately designed to train soldier skills like orientation/map-navigation, hide and seek, capture the flag and even grenade tossing.