I agree that the Leopard 2 A6 is an excellent tank, and I know many others agree with this opionion. Even though the M1 A2 is nearing 10 years in age, it has had several updates.
In the aspects of armour it is still overall the same, but in battlefield communications it has seen several updates, especially, with the IVIS system. The system allows information to be quickly exchanged among tanks on the field, which allows commanders to use their assests efficiently and quickly. In battle this allows the M1 to usually be the first one to engage a target. Also the M1 has one of the best fire control systems. Meaning when the M1 fires at a target it hits dead on.
Though I wish that in futre updates the M1 would have better mine protection and a more powerrful main gun.
With regards to the M1 being a gas guzzler this is very true, however this allows the M1 to get to the engagement quicker. On the other hand it does mean that supplies line have to be stretched to support the M1
Final point the M1 has been proven in battle. Though, I believe that any tank is only as good as her crew. The U.S. Army has the most receint battlefield experience. Giving the U.S. a great source of combat veterans, also the training is top of the line. NTC being an excellent place to train crews for the conditions that future wars will be fought.
I think in the end its almost a toss up between the M1, Leopard, and Challenger II.