Air flow meter compensates for things like differing engine capacities, because its actually measuring the amount of air entering the engine. Problems with air meters is if you have an air leak, you have unmetered air entering engine, so therefore you will run lean. MAP sensors actually measure manifold pressure, so air leaks arent a real issue, BUT, there is no compensation for engine wear, engine capacity increases and so on. Air flow meters are the better of the 2, which is why most manufacturers that have used MAP sensors in the past have all gone back to air flow meters...