While I love my shermans, the next GV's should definitely be something different then US Armor.
I nominate the Churchill Tank. Specifically the Mk. 4, 7 and 8.
Mk. 4:(1,622) The IV was the most numerous Churchill produced, and was virtually identical to the III, the largest change being a return to the less costly cast turret. (Mk. III weilded a 6 pounder (84 rounds))
Mk. 7:( 1,600 with VIII) The second major redesign from previous models, the VII used the 75 mm gun, was wider and had much more armour. It is sometimes called the Heavy Churchill. This version of the Churchill first saw service in the Battle of Normandy, and was re-designated A42 in 1945.
Mk. 8: A Churchill VII which replaced the main gun with a 95 mm howitzer (47 rounds).
Refitted previous versions. (Could be usefull for knocking down buildings and hangars. I suggest it just be a different package for the 7 though, instead of being an entirely different slot.)
The reason I nominate this series of tanks, is because the Brits really only have one tank to call their own, even though it is just a variant really. This would give the Brits 2 tanks, the Germans 2 tanks, the Russians 2 tanks, and the Americans 2 (not including the M8)