Always standard. I haven't got the time for a longer game, I've even become someone who doesn't finish games now, once I know I will win, I stop. (two kids just seem to eat time. I used to have 12 hour straight sessions of previous civ games)
And I don't enjoy how little time you get with things on the quicker speeds. Sure I can build those mamaluks in a shorter time frame but I can't move across hexes any quicker.