The battle of Marathon 490 BCE.
Marathon - it was the Athenians.
The Medes.
First you must define what 'best' is - in what aspects.
They absorbed the Medes, their previous rulers.
The Battle of Marathon was the first attempt , and first defeat , by Persian forces to subjugate Greece . The Persians were defeated by the Athenians at Marathon , Greece .
They were leaders the Persian Empire. Darius was the father of Xerxes. Darius led the Persians in the first Persian war, while Xerxes led the Persians in the second Persian war.
The Battle of Marathon was a turning point during the first Persian invasion of Greece. The Persians vastly outnumbered the Greeks on the battlefield, but the Greeks were able to defeat them. The Greeks charged the Persian troops with a thin weaker line, while the Greeks' left and right flanks consisted of stronger troops who quickly surrounded the Persian troops and attacked them on both sides. It was a crushing defeat for the Persians, and the battle convinced the Greeks that while the Persian Empire had vast armies and archers, it was possible to defeat them.
The Medes, who had been ruling them. They combined their forces and took over Babylon and moved on to establish their empire.
Ottoman Empire, Cezzar Ahmed Pasha in Egypt.
The armies and navies of two dozen southern Greek city-states, led at first by Sparta and later by Athens.
The Persians in the 6th Century BCE established a road system to link those parts of the empire not accessibly by sea.
They had been a subsidiary of the Medes until Cyrus took them over and used the merged power to move on to take over the Babylonian Empire and beyond.