I think one should make a distinction between the in technical /cabability terms "best" and then the most "important" tank.
In the technical/cabability discussion Pz V and VI must be ranked very high. Panzer V somehow represent the sum of german tank design resulting in a very good all rounder which stroke a good compromise between armour, armament and mobility, while Panzer VI, when it entered service in mid 42 did not have it's equal on the battlefield, assuming it was up and running...
In the "most important" discussion T34 can be rated as number one, sherman is allso quite high on my list, while I would pick Panzer IV and STUGIIIs as the most important german tanks.