I'd be inclined to agree on the Tiger as the best heavy tank but I depending on your definition of "best" a case can be made for the IS series.

As for medium tanks I'll go with the T34 and M4 being too close to call. The 17lber however is only an advantage vs the cats. A tank so armed isn't as well equipped to deal with the more common threats and tasks as the other M4 variants. One of the strengths of the M4 is all the different armament variations.

For light tanks how about the M24.