Ukraine

They are basically a custom hybrid roughly around Leopard-2A5 and A6. They have electronic and armor upgrades on A6 level (maybe even slightly better in some areas) but with still the shorter and slightly less powerful gun of the A5 (also some adaption for better performance in harsh weather that might come in handy).

Given the geographic reality of Ukraine, the gun shouldn't make a big difference as the pattern of wide open fields parted by smaller strips of forest usually limits the tanks to ranges below their max range anyway.