I have a 2000 A6 4.2 Sport. It is both the best and the worst car that I have owned.
Best - This car is an incredible touring car. More comfortable than anything I have ever driven on long drives. Gobs of power and still quite economical. I averaged 75mph on my last trip to Fla and got 24 mpg. It is built like a tank - my wife has several times commented on how much more safe she feels than in other cars we have owned. Plus, the Quattro system makes the car incredibly sure footed, even in snow with wide performance tires.
Interior materials are unmatched.
Worst - I bought the car used with a CPO. Before I bought it, the transmission and radiator had been replaced. After I bought it, the automatic steering column adjusting system had to be replaced. It turned on a fault code for an "out of time" fault resulting in a three week stay at the dealer where the had the engine out and the heads off. Never did get a straight answer on that one. Most of my heartburn came from crummy dealer service.
Last week another fault came up and it appears that I have a burnt valve. this repair is being addressed by an independant since it is out of warranty (76,000 miles). I am hoping that we find a socket in the exhaust port from when the dealer worked on it!
While we are in there, we are addressing some coolant hoses, the cam belt and any other major service items, so I am likely looking at $3000.00.
That being said, if I can get another couple years out of it, I will be fine. In the back of my mind is the transmission because when that goes, it is basically game over. Also, the A6 has a silly number of joints in the front suspension which can get rather salty to replace.
The Audi is a great driving car. I tell my friends who ask about it that the smart man buys a Lexus, but a car guy buys the Audi and plans for the expenses! My friends at the independant repair shops in the area all tell me to buy a 5 series BMW next time. (the old body style). Not as roomy and teh interior is not as nice, but they are cheaper to buy parts for.