I like Audis - they are nice cars, thats all I need.
EnI, you are asking what Audi have that BMW doesn't. Maybe I'm wrong, but I can't really think of anything BMW has that Audi doesn't, or AT LEAST anything Audi needs to have from Audi.
But since it has come up in conversation, what does Audi do for me that BMW doesnt? Audi has a clear cut futuristic/modern design strategy. To me, Audi has always been the company with the most futuristic/modern cars on the road, and their designs seem to last and age alot better than other cars (take Tumbo's A4 for example!).
But anyway, well done Audi!