Just because Azula was a dictator (or rather, would have been one), and the fact that she is the only person on Avatar evil and scary enough to make the devil himself cringe, does not disqualify her as a "great" person. To use a real history example, Jesus Christ was beyond doubt on of the most well meaning people in history (to the point where he has his own religion). But in a recent pole to find the most influential "great men" in history, Jesus was trumped by Julius Caesar and Shi Huang Di, two of the most ruthless conquerors and most successful dictators in history, who incidently have been found in discussion on the historical comparison thread to be incredibly similar to Azula.
Tell me honestly, would you seriously name your dog Julius Caesar? It is just demeaning.
So while goodness is always nice, it does not always = greatness.