This is getting very interesting discussion. I'd have to go for the Panther myself, as Mitch said once it was over its teething problems it was an awesome weapon. Speed,firepower and well armoured it was perhaps the pinnacle of German AFV design. The T34 also deserves mention I believe, sloping armour, a good gun, reliable and with wide tracks it was a good in mud and snow, an excellent all round Tank. It was produced in large numbers and at great speed, it wasn't a 'pretty ' Tank by any means, David Fletcher of Bovington Tank museum described the welding on it that 'Would make a German Tank designer weep' , but that wasn't the point, tough and powerful it played a large role in final victory.
Difficult to argue against the Jagdpanther as best Tank destroyer, apart from two problems of limited gun traverse and its wheels needing time consuming maintenance it was another classic German weapon, but the five hundred odd that were made were eventually swamped .
As for the Brits, anything that had that 17pdr was going to be a real threat. the Firefly must have come as a rude shock to German tank crews, suddenly the mighty Tiger was not unbeatable.
Rob