If you don't mind taking the occasional artillery round in the face, a broadside shot (aiming for the driver's position) is normally a 1 hit kill against panzers. Firing into the rear works decently well (normally getting the engine or turret), and occasionally landing one underneath the tank (as in a low six approach and you miss) will knock out the engine.
There's an oddity with the flaks where, when attacked from one side, the tracks on the other side will be shot out. I still am able to kill them as outlined above, but I get shot a lot more trying it. From above and behind is normally a little safer, as the driver is often looking forward more than backward.