Ok for almost years there was conjecture on whether or not it was Obito or, as I thought, Danzo was really Tobi.
Now that the ultimate bomb has been dropped we are right back at the same question.
The man claiming to be Madara is not Madara.
Despite having seen him die, I'm still going to go with Danzo on this one. Same hair, same single sharingan in the SAME eye, and same politics.
It honestly seemed odd to me at the time that Madara had turned on such a useful ally, one that was willing to sell the Leaf out for his own goals.
Madara and Danzo were not at the Kage summit at the same time.
Now it's hard to see how he could have pulled off a successful illusion against Sasuke, but I'm always suspicious when someone dies in an explosion.