It's hard to answer your question without knowing what the need is,
If your wanting to destroy objects with HE and such,, the M-4/75 has a fast rate of fire, optional rockets and it's HE round is probably the most effective in the game.
The panzers are great for learning in tank v tank as well as bountiful perk earners,, the M-4/75 will also earn perks fast,
The t-34/75 is also good for tearing down a city but it has a slower rate of fire than the M-4,, it does make up for it with better ground speed and a better survivabilty factor
The T-34/85 is a good all around tank, a lot of players use it for tank v tank with great success,, it is an inexpensive hard hitting and durable peice of equipment
I'm fond of the M-18 and the M-4/76 more than most,, both have the same gun and can take out anything in the game from the side or rear, they are soft tho and will not survive much damage from anything with an even average gun,, they have decent rate of fire and the M-18 has speed over most anything in the game except the m-3/75 and the M-8,, it is best used to go around and attack. From the sides or behind,, Shoot,move,comunicate type stuff,, no sitting still in it or your toast,, also keep it out of sight of low flying planes,, it loses it's turret easily and most likely wil be killed with a few hits from most planes in the game,
The heavy hitters are the panther, tiger1 and 2
The tiger 1 has a slow rate of fire and a slow moving turret but it's gun will kill you with one shot if the gunner is good, it is strong out front,, it's really pretty strong all around,, it will pivot turn to help with its slow turret ,, it is best killed from the sides and or rear
The panther is faster firing and it's turret speed is improved as well,, also it gun range is much better in the vertical,, hull down/ up positions are best,, it's front is it's strongest area,, don't let anyone get by you or your toast tho,, it is weak in the sides and rear about like the panzer
The tiger 2 is just a beast,, big gun, long range' tough as nails all around,, keep a lookout for M-18s sneaking around you,, much like a 262,, if your in a Tiger 2 most people seem to forget everything else and try to kill you no matter the cost, I like to kill these with the M-18 from very close range directly behind and it usually takes a couple of shots
Hidden jewel--
The Sherman firefly,, in my opinion the most fun tank to use, slowest tank in the game but,,,great gun,(same as the 17lb gun on base) long range kill ability,, very soft tho like all M-4s,, the trick with it is to make sure know one knows that's what your in,
Other than its slow speed, the only thing bad about it is it's rangefinder is obscured when zoomed in, it's hard to hit targets at extreme range in the zoomed in position,, once you are used to it tho, you'll figure it out!
Hope that helped,, I didn't add anything on the tank destroyers but they have the same respective guns of their German tanks do the ability to match as well as some good up front armor,, very soft in the sides tho