Depends on your criteria - if it was a case of which one would I want to go to war in then the Merkava would come out on top (sorry chally fans, but the driver can't always escape if the turret is in the wrong position...)
T34 was a war winner because it could be turned out cheaply and quickly - check the casualty rates for the T34, they are truly staggering! If the Germans could have built Panthers at the same rate as the T34, they would have driven the Red army into the Pacific Ocean! It had some serious deficiencies that could be exploited once you knew what to shoot at, and the material quality suffered later in the war as they tried to boost production.
Same goes for the Sherman, altho the M51 did stay combat effective long after the T34/85 had ceased to be...
WWI tanks had the same effect as Hanibal's elephants - shock value only, easily dealt with if you have the right weapons and tactics
T54/55 was a death trap - the fact Israel kicked the might of the Arab armies to the kerb in 1967 proves this.
Centurian was a good tank in its day, and again the Isrealis showed what could be done when you had to upgrade what you have, instead of just throw money at new toys...
