I'd put down Aquilonia as most roman, but all of the Hyborian realms have a roman touch, Koth being Byzans in my opinion.
Though Argos is linguisticly roman, it's the most greek state in my mind, hellas not being hellas withouth the sea. But of course Corinth is greek too. I suppose Argos is cykladic greece, while corinth is closer to (duh) corinth, delphi, athens and the boiotian city-states.
As for the noble cavalry, that's not as exclusively medieveal as one might think. Assyrian Charioteers and pre-classic Hipparch knights antedated the chivalric knight by a hundreds and hundreds of years.
Ergo: Aquilonia is Imperial Rome, Argos is maritime Greece, and Corinth is the rich, opulent Greece of philosophers and city-states.