they have both different roles and I never had any problems, to fight other tanks with a Panther.
If i see the enemy relies a lot on infantry, I get a brummbar. If I see there a more tanks, I get a Panther.
Well see, the difference there is if you're playing brits:... i see the enemy relies a lot on infantry, I get a Comet. If I see there a more tanks, I get a Comet. :-) Get it? It fulfills both roles at roughly the same price.