"Most decorated soldier of WWII" is such a broad definition it is almost impossible to make a choice. Does a MOH equal a VC? What about the Ritterkreutz?
However Murphy was one of the most decorated soldiers for sure.
There is one major difference between the Allied and the German medal systems. Almost any medal in the British or American services could be won independently of each other; even a VC or MOH could be won by a single act of heroism. The German system on the other hand was progressive: Your first act of heroism won you the Iron Cross 2nd Class. Your second act of heroism won you the Iron Cross 1st Class. Then there were three classes of the German Cross to be won for heroism equaling the Iron Cross, but not justifying the Knight’s Cross. Then for your umpteenth act of heroism you could win the Knight's Cross. Then there were Oak Leaves to be won for your Knight's Cross, and after that Swords, and after that Diamonds.
Only one person managed to win all that and Gold Oak Leaves for his Knight's Cross: Hans-Ulrich Rudel. He was one of only 27 men to be awarded the Knight's Cross with Oak Leaves, Swords and Diamonds, and the only one to be awarded the Knight's Cross with Golden Oak Leaves, Swords and Diamonds. Rudel flew over 2,500 combat missions and destroyed 800 vehicles, 519 tanks, 150 artillery guns, a destroyer, two cruisers, one Soviet battleship, 70 landing craft, 4 armored trains, several bridges and nine aircraft in aerial combat. He was such a menace on the Eastern Front that Stalin placed a bounty on his head. He would be my bet as the most decorated soldier of WWII, regardless of nationality.