German forces preferred to surrender to British and American forces rather than Soviet forces because they felt America and Britain would treat them better as prisoners of war than the Red Army would.
When the Germans attacked and invaded Russia unprovoked, they gave no quarter to the Russians and thus they could not expect any from the Red Army.
Indeed the Russians were so bitter at the massive Russian civilian deaths (1.5 million) and military deaths (1.8 million) and the devastation of their vast country that civility and decorum were thrown to the wind. After the turning point of the War at the battle of Stalingrad, they simply acted as payback time as they pushed the German forces all the way back to Berlin.
The Germans knew it was certain death to fall in the hands of the Red army but at least their lives would be spared by the Americans and Britons.
