I can see why it's hard to choose between these cars but I think it's clear they have different purposes.
BMW give you an aggressive looking coupe, RWD and plenty of power. Will be a blast to drive. Audi give you a more practical car and it still looks great but can't look as good as a coupe (TT-RS comes in at this point if you want to compare coupe vs. coupe). The Audi also has more usable performance for roads/weather conditions and clearly has the better interior IMO.
Like Footie said both cars are great but just do it in a different way. I don't think you would regret owning either.