The M1A2 SEP, Challenger 2 and Leo 2A6 are probably the best MBTs in the world in 2010. How they rank against each other is hard to say since so much info is classified.
In terms of fire control, all three can engage and hit (usually with the 1st shot) a target while moving at top speed. Basically, they can hit and kill any target they can see with the first shot.
In terms of frontal protection, I would give the edge to the M1A2 SEP over the CR2, but that is just based on the fact that a Iraqi RPG-29 penetrated the frontal armour of a CR2 indicating a potential weak spot.
All three have weaker side and rear armour which can be penetrated by any ATGM/RPG.
However, in the real world, a ranking such as this is meaningless, since the army operating the weapon is often more important than the weapon itself.
The German Army, equipped with Pz III/IVs , trounced the Soviet Army in 1941-42, even though the Soviet T-34s and KV1s were much better tanks. The IDF equipped mostly with upgunned WW2 era shermans beat the Jordanian Army equipped with more modern M47 "Patton" tanks in 1967.
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