Exhaust, provided the front of the case has fans set to intake and the case is designed with the rear fan at the highest point of the case, in which case it's due to the fact that the hot air will always rise, regardless of which corner of the world you're living on. Make and model of the case? If you're working with aftermarket fan(s), include their make and models.
You ask, "which way is intake and exhaust?" Look closely on the outside of your fan frame. Usually somewhere on it there will be two arrows. One points around the frame for the direction of fan blade turning, and the other points through the fan to indicate air flow direction. So mount the rear fan to blow out of the case. When you start up, just feel the air blowing (or hold a tissue in front of it) to check which way the air is moving.