I would suspect the T-34 was the most cost effective with the Sherman coming in a close second. I base this on the T-34 being simpler and cheaper to build with an offset that it was shot to pieces more often and required more rebuilding due to its inferior reliability compared to the Sherman. The Sherman cost more to build but was cheaper to operate.
Of course, it could be the other way 'round too.
The Germans don't even get a door prize for cheap to operate AFV. Their equipment was expensive to manufacture, hard to maintain, and just all around costly.