I traded a 1998 A6 Quattro in on my 2001 XC and don't regret it.

The ergonomics of the XC are far better, there were a number of weird and annoying things about the controls in the Audi--particularly the door locks and the automatic climate control.

The XC AWD is more sure-footed. I don't know if that's from weight or tires or what, but the Audi would often start to fishtail when accelerating in snow. It would straighten out quickly, but the XC never does it at all.

The brakes on the Audi were amazingly good and the interior materials are of a higher quality and more durable than the XC.

Both cars have had some problems. The Audi was repeatedly recalled for the fuel guage sensor and twice we ran out of gas due to the faulty sensor (it went from 1/4 tank to zero in a few seconds and the engine died). Audi blamed poor gas quality--yeah, I used poor quality high-octane from fly-by-night companies like Exxon and Mobil. Right. Also, after only three years, the plasma display on the information center was showing noticable dimming around the edges. The heated steering wheel also stopped heating.

The XC has had a bunch of annoying software bugs and the seat/mirror memory is like playing roulette. You never know whether you will get your correct seat setting, or correct mirror setting or both or neither and just because it's correct when you leave the car doesn't mean it will be correct when you get back in, even if nobody has touched it! It has never left us stranded, though.

XC gas mileage is much better than the Audi. I was a bit surprised that the A6 mileage was not much better than my Chrysler AWD minivan (average mpg Minivan: 14-16, A6: 16-18, XC: 22-24).