First you must define what 'best' is - in what aspects.
The Persians were the best rulers for the empire because they were tolerant of the people they conquered. They respected their customs and religious beliefs. They encouraged unity so they built hundreds of roads making it easier to communicate with other people.
Gaining an empire is its own reward.
The Persians absorbed the Phoenicians into their empire, and used their resources.
The Persians
No.
Persians
Alexander the Great conquered the Persian Empire and converted it into an empire of his own, not to destroy the Persians but to convert them to Greek culture.
The Persians conquered the Babylonian Empire in 539 BCE.
He was not mean to the Persians - he led them to form the greatest empire of the time.
An empire.
It expanded the Persians.
They retained traditional local government, while the empire provided security and encouraged prosperity.