Which branch do you think is the most disciplined

I would have to say the Marines also. They have the few and the proud. They seem a little harder on the guys than the rest of us. The Army's discipline is going to shit with the whole politically correct carp.

As basically everyone else claims, the United States Marine Corp.
They are more disciplined seeing as though they go through more rigorous Basic/Boot Camp/Training than any of the others. A fair amount of them also seem to abide by the standards more than the rest due to the rigorous training being drilled into their minds all day and all night.