I have a 2004 A6 2.7T with about 58000 miles on it. I'm wanting to throw a chip on it. Does anyone have any advice about which one is best to use?

 

If you search the A6 forums, you will find tons of threads about chip suggestions. Also, check out the stickied post called something like Tips for the new 2.7T owner" - tons of great information in there.
Personally I went with the APR chip, and I have been very pleased.

 

You'll find chips are like religion, at least on this forum. I've been very pleased with my GIAC installed at 75k and car now has 187k. I was told to install heavy duty diverter valves and throttle body boot at the same time and it was good advice.