Would you buy a used Audi S4 Avant or a used Mazda 3 MPS?

The Mazda - a friend of mine has an Avant RS6 and it has been nothing but very expensive trouble. Recently the suspension had to be replaced - Audi wanted �6000 and he fitted Bilstien for about half that. It goes like you would not believe but he wishes he had never seen it but feels it has cost so much in upkeep he now has to keep it.