frekin Germans know how to built tanks man! I would put the Leo A7+ as numero uno best MBT in the world.
Among the best :
M-1A2 very thick armor on the front but lower on the sides and back,
Merkava maybe the best protected but less mobile / Fast
Russian tanks less lighter about 45t less high and less armored in more few space more tiring for the crew but unusual gun use missiles also since T-64.
Otherwise the better Leclerc, Chall II, K-2, Type-99 ( Type-96 as Russian lighter.. ), Ariete, Type 90 and very new Type 10 lighter as Russian but use much ceramic in, Her gun 44 cal as Type 90 and some others
Guns/caliber :
All Soviet/Russians, dérivatives Type 91... 125/48
Leclerc 120/52
Type 10/90 Leo 2 A4, M-1A1/A2, Ariete Merkava III/IV, K-1A1 120/44
Type 96, Al Khalid 125/48
Type 99 125/50
Leo 2A5/A6/A7, 2A4CHL, K-2, Altay 125/55
Arjun 120/?