OK, here's a partial listing of possibilities...
M4 (original welded hull, 75mm, lots of these still in use by 12/44)
M4 "composite hull" - rare in US use in Europe but they were there - more common in British/Canadian use
M4A1 - cast hull - also lots of these still in use
M4/M4A1 with dozer blade - 75mm tanks with M1 dozer kit
M4, 105mm howitzer - the only radial engined version in the "wet stowage" type hull
M4A1 76mm, Wet Stowage - quite a few around, especially in US 2nd and 3rd Armored Divisions
M4A3 75mm Wet stowage - a common replacment tank in the fall of '44
M4A3 76mm Wet Stowage - the M4A3 with the larger turret and 76mm gun, quite common in the ETO, especially in Third Army units.
M4A3, 105mm howitzer, this and the M4, 105mm were in the Assault Gun Platoons of each tank battalion
M4A3E2 - the "Jumbo" an up-armored "assault tank", 254 built with 250 going to the ETO starting in the fall of 1944.
M4A3E8 - just started appearing before the campaign started, more showed up for the counteroffensive in 1945.
M5A1 light tank - about 20-25% of the tanks in ETOUSA were light tanks
M24 light tank - first batch had just reached Europe before the Battle of the Bulge with more comming in 1945
M31 tank recovery vehicle - based on the M3 medium
M32, M32B1, M32B3 tank recovery vehicles - based on variations of the M4 tank
M10 3" gun motor carriage - the most common tank destroyer in Europe in 12/44
M18 - the lightweight 76mm tank destroyer
M36 - 90mm gun motor carriage - started appearing in Europe in the late fall of 1944 - the only mobile 90mm gun until the arrival of the "Pershing" tanks
M8 75mm howitzer motor carriage - an assault gun based on the M5 light tank, used in Mechanized Cavalry and Armored Infantry units.
M7 105mm howitzer motor carriage, the "Priest", appearing in every armored division plus some seperate battalions
M12 - SP 155mm gun
This is a quick list of the primary US tanks in use on 12/16/1944. I didn't list armored cars or halftracks, etc. The underlined ones have been produced by K&C. I didn't count the K&C "classic Sherman" M4A1 as it is an "odd duck" that would actually be more common in the Seventh Army, not common in the "Bulge" combat. The Strictly Limited "General Inspection" Sherman is an M4A1 76mm Wet Stowage under all the sandbags. K&C also did an M4A1 76mm with the wide tracks (HVSS) as DD27, and they did a rather mediocre (by current standards) M4A3 75mm Wet Stowage in the original Bulge series.
Note - don't worry about "whitewashing" or winterizing all your tanks. Most units operating during the initial German attack were in standard OD or OD &black colors. They didn't have time to repaint before they were deployed to meet the surprise German attack. The white paint jobs mostly came later when the Allies counterattacked the bulge in their lines.
Lots of possibilities out there and I think Andy has a desire to produce many of them if we give him the time.
Gary B.