The most commonly used aircraft used by the US Army for paratroop drops in WW2 was clearly the Douglas DC-3 and its derivatives. This aircraft was known under many military designations (mostly due to variations in engines or source of the aircraft-- e.g. taken up from civil airlines versus purchased from the factory). The standard military designation was C-47, though other near versions were the C-53, C-48, C-49, C-50, C-68, and C-84. But in practice, all of these were essentially C-47s with relatively minor modifications. These were used in all theaters of operations. Though the C-46 had a larger carrying capacity, the majority of these aircraft were used as cargo haulers flying "over the hump" of the Himalayas, and thus were used rarely for paratroop operations. In the first large-scale use of paratroops, the Sicily invasion of July 1943, nearly 4400 paratroops were dropped. During the D-day invasion, over 60,000 paratroopers were dropped, almost all from C-47s. There were many other airborne operations, but in all the C-47 played the major role. One other aircraft which cannot be skipped in this discussion is the Glider-- These were used for landing troops from the air into enemy territory, but not by parachute. The Waco CG-4 was the most common, and could usually land 15 fully-equipped troops, with weapons and vehicles. I do not have any estimates at hand of the actual numbers of glider-borne troops which were actually deployed by this means in WW2, but it certainly is nowhere near the number who parachuted from the C-47s and their brothers/sisters. There are lots of good references on this subject, though I would recommend F.G. Swanborough's "United States Military Aircraft Since 1909" for more details on the C-47 and its derivatives.