I would say Stalingrad also, it holds the Guinness World Record for Bloodiest Modern Battle; "The greatest death toll in a battle has been estimated at 1,109,000 in the Battle of Stalingrad, USSR (now Volgograd, Russia), which started in the summer of 1942 and ended with the German surrender on January 31, 1943. Approximately 650,800 Soviet soldiers were wounded but survived.
Many experts consider Stalingrad to be the crucial turning point of World War II. The battle, which raged fiercely from the summer of 1942 until January 31, 1943, marked the fullest extent of Nazi Germany's incursion into Russia. Stalingrad, because of its commercial and industrial importance, was seen as a major prize.
One obvious reason behind the battle's terrible destructiveness was the importance of Stalingrad. Russian soldiers were ordered never to "take a step backwards". Stalin, the Soviet leader, knew that losing the city that bore his name would be of immense symbolic and military significance.
Hitler, the German leader, was equally determined. He showed a lack of military judgement by not allowing the Nazi armies to retreat even when they were almost completely encircled by the Russians. The Germans were made to remain and face near total annihilation by the ultimately victorious Russians."
Also the condition of the city with all of the house to house (CQB) combat would be a surreal experience. Don't forget there wasn't any set tactics for room clearing. Plus the amount of overall military units in the city would help place it as the Fiercest Battle in History. At least in my opinion.