A difficult choice, I see. Either way you can't go wrong. The 2.8L 30v V6 is excellent and the 1.8t is very smooth as well. However, I do hope you are getting the Quattro.
If getting a '98, you might want to get an early '98 rather than a '98.5 as something in the rear suspension on the later ones is not as beefy and could crack. I don't remember exactly what it was but you should be able to find the answer at
http://www.audiworld.com Another thing to keep in mind is that the 1.8t is geared a bit shorter than the 2.8. My friend has a '98 2.8Q MTX and his 3rd gear is almost as tall as 4th in the Contique. What this means is that if you chip the 1.8t to the power levels as the 2.8 (~190hp), the 1.8t should still be faster due to the shorter gearing and lighter weight. On the downside, the 1.8t will be turning at higher RPMs on the highway.
Good luck, and let us know what you end up getting.
