When modern people think of Greek culture, they tend to think first of Athens. The most famous philosophers, playwrights, and statesmen were all Athenians, and Athens was the birthplace of democracy. Men who owned land voted on laws, served on juries, and were all eligible to hold public office, regardless of social rank and wealth.
While the wealth of Athens was based mainly on trade, Sparta was always primarily a military power. Spartan citizens concentrated on warfare, while slaves worked in the fields. The Spartans kept a large permanent slave population, the Helots, working for them across their territory and were thus prevented from going far away on their military campaigns for fear of a revolt. Nonetheless, they eventually prevailed in the Peloponnesian war against the Athenians, who had considerable maritime power but could not equal Sparta on land. Sparta was ruled by two kings and a council of old men known as the Gerousia.
Miletus was culturally Greek but was in what is now Turkey. The Greek culture of philosophical enquiry and intellectual freedom began in Miletus, but the city was soon eclipsed by Athens in this respect. Miletus was ruled initially by kings, then by tyrants, assisted by an assembly of oligarchs. Its position in Asia Minor made it the most cosmopolitan and diverse of the three cities, while Sparta was certainly the most insular.