I bought my A4 used about a year ago, and I have fallen in love! There is no other used car out there that can match the fun to drive, reliability, build quality, or fuel economy for that matter. I can manage around 20-24 around town, and at most 28 on the highway, that's pretty good, considering its a 15 year old car with 215,000 miles on it, with a V6, and Quattro. Like I said, it has 215,000, and it still runs like a dream. The only problem I have had with it is an EGR code always popping up, I went thru the whole EGR system, and couldn't find anything. Turns out it was the filler hose on the gas tank, sense it also leaked when I filled it up.
Definitely the hallmarks of Audi, their absolutely fantastically well laid out interiors, and the build quality of them, amazing. Like I said, 215,000 miles, 15 years old, and not a single rattle or squeak. The other, has to be Quattro. I know I don't take full advantage of it, but I love to go around a corner at 50 mph, and not have to worry about a thing, because I know the Quattro will keep my right on track. I also LOVE the 5-Speed. This car WOULD NOT be the same with the automatic. After owning this car, I promised myself that I would never own an automatic, EVER. There is also a surprising amount of space in the trunk too, as in, it's almost as big as my grandparent's Town Car's trunk.
If there is one thing I don't like, its the stupid center console. The top is held on by two little hinges that stick into the side of the console, and it's constantly breaking. In fact it's a good thing they redesigned the whole center console in the newer cars, because the whole thing was just way too flimsy. My brother had a 2003 Jetta, and it was the same center console. It "recommends" Premium, but I just blew it off, why would I use Premium when I don't have to? Well, out of the blue one day, I decided to use Premium, I saw a large jump in both performance, and fuel economy. Plus, the A/C KILLS the fuel economy. I only turn it on once a month now, just to keep it working.