I have the previous Gen A4, and have driven the new ones. The A4 is a superb car, Audi make superb engines also. Audi diesels are in my opinion the best you can get. Nothing can compare.
I myself had a loaned c220 CDi with the AMG trim. V.Nice car, but interior trim looked too plasticky for my liking. Power-wise? The car seemed fine and punchy, but it was not as torquey as its A4 counterpart.