'98 a6 2.8 quattro
I just got a set of tires and Wow.
The previous tires were Pirelli P6, and they were loud and lasted only about 35000 miles.
A blow out forced me to make the change. I sure did not want to spend $615 on tires at this point in time, but it is almost like I just bought a new car for $615! The new tires are Michelin Energy.
On not even a smooth road, but a pretty smooth road, there is absolutely no tire noise. The difference is amazing. The car handles much better. It just about drives itself now.
I'm very pleased.

BTW, I went ahead and spent the extra $20 for nitrogen in the tires. I like to think it is making some difference too.

 

Good to hear you're happy with new tires. Just a side note on the Nitrogen, regular "air" that we breathe and pump into tires is actually mainly nitrogen anyways, that extra 21% nitrogen that you get doesn't make a big difference at least to me but thats just my $0.02.

Either way, whatever tires you have just make sure to check for proper inflation.