I'm surprised to be the only one who voted Korea. I know that Protective isn't that great, and the Seowan is not that great, but it has to beat Japan! The Hwacha is just such an awesome UU, just look at the thing! Your firing Rockets at ancient archers! How is that not awesome?
I've never been overly fond of the Immortal, but Darius is truly awesome, and I think the Fast worker under Asoka is pretty nice. But jeez, Japan and Arabia are not better than Korea.