I saw a program on discovery, the top ten MBT in the world. Basically, all the tanks have problems.
The Merkava is apparently excellent in Israeli terrain, and urban situations, but its weight and poor fuel efficiency make it unusable for expeditionary forces.
The Abrams gets a prety good qrap, NATO interchangable etc, but it runs on a jet engine, meaning its fuel efficiency is terrible, and it has weak spots, like the exhaust, that can cause the bugger to....explode....in one hit.
The challenger got a good wrap, mainly because its battle tested and its armor is awesome, but its not user friendly.
They rated the Leo II number one because it has reasonably good armor, excellent weapons and comms systems, is fast, has good fuel economy, its compact but most importantly it is easy as to drive. Easier than a car apparently.
Check out the show if uve got cable, they do the top ten of some of the coolest machines and stuff.