I'm leaning towards the Soviet T-34, but admit to a certain fondness for the Tiger I and the Panzer IV
http://en.wikipedia.org/wiki/T-34
I love the T-34. Great speed, protection, maneuverability, easy to mass-produce, and excellent gas mileage. If the Tiger was easier to produce, I might have to at least call it a tie, but no, lol. I'm not voting for any American tank, that's for sure, lol. Wasn't the Sherman nicknamed 'the ronson' because 'it always lights the first time?' Ahaha. What a piece of crap.
Sidebar - I wish that we used the Churchill tank with the chains attached to a roller that rips up the land to discover mines in Afghanistan. The roads aren't paved, anyway, and it would scare the crap out of the Taliban, etc. Cheap, too, lol.