The T34-85 is probably the best tank overall. The T34, or the Panther. I never use either though. I favor the M4A3-75. If I get within 5k of a vehicle base I can kill the entire base in less than ten minutes (my personal best time is four minutes). All hangars, all guns, everything, but it will require at least three vehicle supply boxes so that I have enough rockets. I have tried to teach the method to other users, but it is a hard concept to grasp. I don't like killing the base though, but I do like encouraging the enemy to come shoot my M4 where, surprise!, they meet my Tiger II.
Next is the TigerII. Nothing makes people whine quite like a TigerII will. Even if they manage to kill you, they will whine about it because instantly you are back with another one. They are whining about it now on the wishlist forum, because they cannot bomb a TigerII from 35k. The TigerII is the best idea Hitech ever had.