I normally do Monarch, with a few games on Emperor now and again. I'll probably start on the middle difficulty in Civ 5 so I can get used to the game, and will begin increasing difficulty so I can guage how big a difference the difficulty levels make. That's important for multiplayer, so that I know how large of a handycap will be appropraite with different people. I'm sure I won't be able to play the same difficulty level I do now immediately. There will be all sorts of new strategies to develop first.