Julius Caesar isn't on here. Caesar is in kind of an odd place, because he's usually not counted as one of the Emperors - most count his adoptive son/grand-nephew, Augustus, as the first Emperor; as Julius Caesar adopted the (traditional) republican title of dictator.
But he'd be top-tier if he was here. A merciful man of the people, one of the most brilliant military minds of all time, who conquered one of the largest provinces of the Empire? Man had an ambition problem, no doubt about that though.