I've seen some really old plants and they've all used pulverized coal, since it burns more consistently. It basically explodes when it ignites due to the temperatures involved. Coal and gas are both really good at responding quickly to varying load requirements.
I imagine all the new ones use it, and thus all the new ones can change their outputs in a matter of minutes, instead of hours. But that still makes coal one of the slowest sources to react to grid volatility, and sill basically useless to compensate wind oscillations, only useful for the solar cycle.