Water to air can be more efficient... but it eventually becomes limited by ambient temp just like an air to air... what do you think cools the water after it sucks all the heat from your compressed air... it's the ambient air.
Water/Air IC's are typically used in one-shot cars like drag cars so they can pack them with ice... or in the case of the contour, cars w/o a good spot/room to put an air/air.
