I would call the French Maqui one of the great elite units. They were like a ghost, and when the Nazis thought they were safe, the Maqui were tinkering with their planes/tanks/transports if not assassinating leaders. I think the British (I think mostly Scottish) SAS was a great elite unit. You Americans had something, I forgot what it was, where William Colby accomplished many missions. And yes, many Russian Units were excellent (more of my biases). But I would have to say, THE MOST ELITE UNIT in WWII was Pavlov's platoon. Sgt. Pavlov, along with I think 12 people held a house, and a large on at that, I think 4/5 stories for 59 days against German attacks. They held the house, later nicknamed "Pavlov's house" until Russian reinforcments arrived.