I prefer marathon with increased research times. The main problem I find with it is the barbarians are not much of a challenge compared to faster times, even on rabid or absurd or whatever the harder setting is called. Also the civ ai's are easy to deal with on marathon, which kind of sucks. I have to go emperor or deity to get a challenge, but then of course I can usually say goodbye to wonders, which takes a lot of fun out of the game.