I have recently changed from an A5 to an is250. The Lexus in my opinion is a superior vehicle. Don't get me wrong the Audi is beautifully built but the ride is far too hard, or maybe I'm just getting old. Also the spec you get for your money in the IS 250 is fantastic and I love the smooth v6 engine. Having a proper back seat is a real bonus for me as well. If you can put up with mid 20's mpg I would say go for the Lexus. But which ever you choose you will have a lovely car.