In AH I really like the Panther. At long ranges it is tough to beat. It is fast enough to move, reloads fast enough to win a Mexican stand off, and has enough armor to shrug off all but the big guns outside of 1600 yards. The Tiger is a close second but it is really handicapped by a horrible turret traverse rate.
In the actual conflict I am partial to the Cromwell when it was armed 75mm gun with APC M61 ammo. Its speed, mobility, and enough gun (with the HV AP ammo) made it a force to be reckoned with in Western Europe. A close second is the German Panzer Mk IV H, it had so many great qualities and even at the end of the war its 75mm gun was still superior to the US 76mm and Soviet 85mm. I sometime wonder what would have happened it the Germans would have poured money in to the Mk IV instead of the wasting funds on the wonder tanks that did nothing. Yeah, some people and analyst think it was already maxed out, but I think a redesign of the hull armor and frontal turret armor would have done more good than the wonder tanks that did nothing. Then again, Germany was running out of tank crews rather quickly. Hindsight is 20/20.