If I’m just starting the car up, I don’t have much choice, as has been pointed out. It’s cold until the engine warms up. In cold conditions, I’ve found that warm or hot air works most efficiently. I have had people adamantly insist I should use cold air, but I have experimented and it would seem that warm air defrosts things quicker. This makes sense to me because if you warm up the glass, no condensation should then form. It seems to me that using cold air on the glass is counter-intuitive (unless we are talking about hot, humid conditions).
“Condensation on a window occurs when the surface of the window is cooler than the “dew point” temperature of air in contact with the window. Condensation is a result of a combination of surface temperature and moisture in the air.” (via)
On my car, the defroster setting uses the A/C system, regardless of temperature. This is convenient sometimes, other times not (such as when driving long distances, I suppose my choice would be not to use up extra gas for the defroster). But oh well.. small quibble, really, since my car is a champ at defrosting and I’ve ridden in some where you couldn’t defrost/defog the windshield no matter how much you tried.