I only play on marathon. If there was a longer setting I would use that. But I think that is because I like to play a single game for months, something of an actual human civilization simulation. I don't like to treat it as a quick victory game.
Also, I can't stress this enough, in my opinion Civ IV is still the best Civ game and you should try it with the Caveman2Cosmos mod.
There's an ultra marathon mod for civ 5 that was 3x longer than marathon, but it does get slightly unbalanced in some ways late game if I remember correctly.
shmoodow's comments