Red Army = most effective force !

[Marcello]

"Upon its introduction T-64 would have a counterpart in Chieftain, designed with defensive battleas against vast numbers in mind, whose gun would do a nasty thing to
T-64."

King Tiger clause applies: IF you can get it there. To be honest I have heard fairly nasty horror stories about early T-64 reliability but AFAIK it was reasonably debugged by the T-64A/B. The Chieftain had good armor and firepower, mobility was more problematic.The T-64 was more balanced hence why I gave it the "Best" rating. The Leo1 Marder comparison has merits but I would say that the Marder isn't the first thing that comes to mind if I try to come up with the opposite of expendable.

"There IS a reason why for a long time primary AT round in Soviet tanks was HEAT despite its crappy accuracy."

Against steel armor it had good penetration which retained even at the maximum range, it could be used against soft targets and was cheaper to produce. AFAIK at least for the 125mm gun HEAT rounds accuracy wasn't that terrible. Of course that meant that when NATO introduced very effective against HEAT composite armor the soviets had one unpleasant problem to deal with.