I actually find it is quite easy to take out a Panther with a normal 75mm gunned Sherman or Cromwell or something of the like. Aim for the treads. It's all about tactics though. The game is about realism, not balance. It's not much fun when two tanks go up against each other that have the same armor and gun. Try getting around to the side of the Panthers and Tigers. Stay in concealment and most importantly cover. Try practicing offline on singleplayer or coop with some AI. It really helped me learn where to aim while still having the threat of being taken out. Online is much faster and deadlier though, so don't expect them to be exactly the same.
But, like I said, it isn't about balance. Also, with Bazookas v. Tigers, try to get above them and shoot for the top of the engine compartment. It's seemed to work pretty well for me. Also, Comp B works great when you can get it on the tank.
The funnest way to take out tanks that I've found is with mines. It's incredibly hard without a partner though. You just place the mine(s) and then get the tank to drive over them. It's hard offline and incredibly hard online, but when you get good at it, it's a whole lot of fun.
Just my two cents.
