|I am going to admit this is coming off of some war gaming experience but bear with me as none of these tanks have faced each other is real combat. (The main contenders being Challenger, Abrams, LeClerc, Merkava and T-90). I will admit a slight bias toward the Merkava for various reasons to include it is probably the best in an infantry support role but it also has its shortcomings.
I have come to the conclusion that between among the most modern, up to date versions of the world?s main battle tanks there is no clear decisive best tank. When all things are considered they are all just about equal. They all have some advantage that you may point to that you feel makes your favorite it better than the other but they also have the same disadvantage or lack something that the others may have. I feel this is because they may have been designed to function under different circumstance and met different threats. For example a Merkava 4 with the Trophy system is designed for different types of combat than a T-90 with Arena. Despite modifications the Abrams is not the best tank to support infantry with in an urban setting, etc. As for cost per unit manufacture them in equal numbers and the cost would be about the same. The real difference between them has to be tactics, logistics support and crew training.
So let the flame wars and nationalism begin.
Not that is anything wrong with national pride.