All this Korea/Babylon talk makes me want to try them (I've never played either Civ).
I also need to make the jump to Immortal soon. Maybe trying one of them for a SV on Immortal would be a good first try. Hmm. I also like OCC and Babylon OCC SV could be an option...
I'm trying to get through most of the Civs but there are still a few I haven't tried and I have been saving them for the higher difficulties.
England, Arabia, Babylon, Korea, Siam, Germany, Iroquois, Mongolia, Austria and Russia are all Civs I still need to give a try.
Suggestions? I guess I could also wait for the next GOTM or Immortal challenge - if they look good