Both of them, actually.
German engineers loved to make things overly complex, which made mass production and matenance difficult.
For examply, to replace damaged bogie wheels, you had to revove the ones in front of the damaged once, sometimes as many five to get at one. Gear drives often broke, on Tigers, you had to remove part of the front of the tank to get at the gear boxes, ect.
Both the Russians and Americans favored easily maintained and relaible armor, their tanks ALWAYS worked, German tanks broke down ofetn.