The Diocletian
Fire Fly
During Augustus' rule Rome experienced the first major military failure - in the battle of Teutoburg Forest, 9 AD. But for example Charlemagne who's ranked below Augustus Caesar, is said to never have lost a military campaign.
On the other hand, he initiated massive public works projects, and greatly expand the borders of the empire via military conquest. His reign began the Pax Romana for a reason, folks.
However, to be brutally honest he was a manipulative, cunning autocrat who fooled the Roman Senate and people to basically make him emperor.
You decide.