Ello Stuart and welcome on board!!! I assume that the car is standard in terms of brakes??? Dont forget that the A5 and S5 are quite heavy cars so they will never stop on a sixpence. You ask about pads and there are many trains of thought from EBC to Ferodo to Brembo et all, note too that you really need to ensure that your pads work well with your rotors so if you want to replace both then best to fit Brembo pads with Brembo discs.
You may even want to consider an upgrade to RS brakes, for instance.