I would say its a tie between the 101st Airborne Divison Fort Campbell, Kentucky and 82nd Airborne Division at Fort Bragg, North Carolina.
Its almost impossible to compare the two cause of their long and proud history.
I would offer the opinion that likely the most decorated US Army division would be the 3rd Infantry Division. There were 16 million Americans in uniform in WWII, and among these there were around 470 Medals of Honor awarded, in all branches. 37 were earned by members of the 3rd Infantry Division. There were two MOH men in the 101st Airborne, and two in the 82nd Airborne. There were over 11 million men in the US Army and the US Army Air Force in WWII, and among these there were around 5,000 Distinguished Service Crosses awarded. Well over 100 of these went to men of the 3rd Infantry Division (37 for the 82nd; 56 for the 101st). There were also over 4,800 Silver Stars (898 for the 82nd, 456 for the 101st) and over 8,100 Bronze Stars, 50 Legions of Merit and 172 Soldiers' Medals awarded to 3rd ID troops. Part of the reason for this is that the 3rd ID spent more time in combat than possibly any other US division, Army or Marine, with 531 days in combat. The 82nd Airborne spent 422 days in combat and the 101st (which saw no action before the Normandy landings) 214. The cost of such prolonged action for the 3rd ID meant that the division suffered far heavier losses than any other US division, Army or Marine, with over 6600 men killed and 27,000 wounded. Table of Organization for WWII Infantry Divisions was around 15,000 men.
Overall 51 men of the 3rd ID have earned a Medal of Honor. During WWI the most MOHs went to the 30th Infantry Division, a National Guard Division from North Carolina and Tennessee.
Proponents of the famed 442nd Infantry Regiment, the very tough Nisei (Japanese-American) US regiment which fought in Italy, with the attached 100th Infantry Battalion (another Nisei unit) like to claim the distinction that the 442nd was the "most decorated" US WWII regiment. Strictly speaking, this is true. However, unlike every other US regiment, Army or Marine, the 442nd had SIX infantry battalions. Every other US regiment had three, meaning the 442nd was twice as large as all other regiments, so you might expect that its members would earn about twice the medals as any other regiment which also saw hard service, and this is the case. Together the 442nd and its attached 100th Bn amounted to 7/9ths of a division, basically, as far as rifle strength goes, and were never a part of any division.