Well it can't be the best Adler, and thats mainly because its been turned down by nearly every country which has been offered picking it as their MBT, in favor of having the Leo 2A5-6 instead.
And also since the M1A2 Abrams has been losing every single trial between itself and the Leo 2A5-6, in everything from firepower to armor protection to overall battlefield efficiency, the Abrams just can't be crowned the THE best MBT in the world today.
I'd bet all my money on either the Challenger 2 or the Leopard 2A6 in a fight with the M1A2 Abrams, or any other tank for that matter.
Now I'm not saying the M1A2 Abrams is a crappy tank or anything like that, as it sure proved itself very differently in both Gulf Wars. But the Abrams is however marginally behind the Challenger 2 and Leopard 2 in the running for being crowned the best MBT in the world.
And this is not just a personal opinion, this is what most experts on armor would agree with...