The German tankers were by far the best in the world 1939-1942, but eventually after some very bitter lessons, the allies eventually caught up in most aspects.
The American tankers in an amazingly short time, and with little experience, bettered the Panzers at El Guettar, Arracourt, the Mortain offensive, and the Bulge, It showed that Americans quickly learnt the ropes after Kasserine.
And where the efforts of tanker aces like of Wittmann, Barkmann and others were honed by many years of hard fighting in Poland, France, the Balkans and the Eastern front, the little known exploits of American tankers like Staff Sergeant Lafayette G. Pool, who again with little experience in tank warfare, [and was fighting against Panthers in his hopelessly outclassed M4,] is credited with 258 vehicles destroyed, 250 German prisoners of war taken, and over 1,000 dead before the guns of his tank, IN THE MOOD.
By all accounts the top Russian ace was Guards Capt. Samokhin Konstantin, 4th Tank Brigade, in BT-7's, and T-34's, died in 1942 with 69 kills + 13 other AFVs, 82 guns, 117 motor vehicles.
Although Lavrinenko Dmitriy (T-34, 4th tank brigade) is some times mentioned as the top Panzer killer.