Rank 1- LVT A4
At 1.3 the 75mm will destroy anything. With overpressure the He rounds will make all of the light tanks explode.
Rank 2- M4A5
It's basically a Sherman with slightly better armor and the British 57mm gun. Not too expensive, and the gun is pretty powerful.
Rank 3- T20
A great tank, it's small and has decent armor with a powerful gun. At 6.0 the gun gets a little less powerful but it's still a great tank.
Rank 4- Super Hellcat
It's basically the Hellcat but with a 90mm cannon. Is a bit expensive but is really worth it.
Rank 5- T54E1
Has a 105mm cannon with a 5 sec autoloader. At 8.0 you'll see more APFSDS, and it's a bit expensive, but the other parts of this tank make it very powerful.
Rank 6- XM1 GM
The prototype of the Abrams. A very capable tank at 9.3. It also has pretty decent armor.