Sparta VS. Athens
Athens and Sparta are the typical opposites which show how two different societal structures can work. The Athenians were a very democratic and closest at the time to our type of government with voting and structured law. The Spartan society was very militaristic and would coincide with Darwin's expanded theory of "survival of the fittest." The Spartans were a powerful force, but secluded to many of the population and could not keep up these old ways of singling out "perfect" soldiers since they eventually declined due to a shortage of warriors and increase of Helots. The Athenians also had their own flaws such as they're overly peaceful ways which at that time would have weakened their hopes for expansion compared to Sparta's aggressive nature.
If I could choose to join one of these nations it would most defiantly be the Spartans. They are a much stronger nation and better suited for that time. For me, It would be easier to assimilate into their culture of a military view since for me I do plan on joining the military and all my steps before that are to prepare me for this. Not to be perfect since no one can be, but to prepare myself as much as possible. So, their culture would fit along side my modern day thinking and I would enjoy at least living a day in the Spartan military.