In my opinion, hands down, BMW. Drive them both. Audi has a long way to go if they want to "overtake" BMW they have a lot more to do than launch one good car. They need to completely re-vamp their mission.
They're different cars. Audi is a really excellent VW. They spend a lot of time building a full line of vehicles: suvs, economy cars, luxury cars, sports cars, and every imaginable type of vehicle. BMW has been fully focused on building enthusiast road candy since day one. Don't get me wrong... Audi is an incredible manufacturer, but compared to BMW they can't compete.
The only area in which Audi has BMW beat is suspension geometry, and since they at least dabble in diesel that gives them a nice big point over BMW