Eh, the problem with this, and similar threads, is that there is no one best tank, people stare themselves blind on just one of the tanks uses, that of "tank killer", but tanks are ment to do more than just blow up other tanks, this is why there exists light, medium and heavy's, if tank warfare was only about tank on tank engagements, there would only exist heavy's.
Is the T-34 a bad tank because the Tiger could shoot it? no, it's a very good medium tank, fast, manouverable, reliable, well enough armed in its weight class, it's just not a heavy tank ment to slug it out with other heavy tanks.
Is the Tiger a bad tank because it was slow and heavy? no, just don't try to use it as a light cavelry tank, it isen't one, it's a heavy tank killer.
If you're going to find the "best tank", you'll have to specify "best at what" first, else, it's a bit like arguing that a B17 is a worse plane than the BF-109 because it's no good at dogfighting.