Voted France to see more social policies in action, but I'd certainly be happy with Rome or Germany.
Regarding era, I'd definitely prefer Medieval or Renaissance. Those feel like the most important eras to me, strategically: it's when you're still trying to setup your economy, wage war to gain critical territory, and solidifying your empire. Generally, at least for me, the game is usually over by the Modern Era (and often by the Industrial Era), so it's less interesting. Also at that point, small strategy decisions like "which tile improvement do I make for this square (err, hex)," and "which building should I build first for this city" are relatively insignificant and inconsequential (for the most part).