If I had the $$ I'd buy a Viggen cabrio today. Having said that, I'd agree with PhilS about the interior appointments and torque steer. I shopped the A6 aggressively in 2000 but ended up with a 9-5 and am glad I did. The A6 is an elegant car, esp the interior design. Its refined, smooth, and solid feeling. But the Saab is much more performance oriented and feels light on its feet. You didn't say which A6 model you're shopping for so its hard to offer a clear comparison but being a former 9-5 owner and having compared the two cars very closely, I'm glad I ended up with the Saab.
The 9-3 will feel more dated to the Audi, prolly rattle and squeak more, and may not have all the "wow and delight" features you want. But the 9-3 will be more involving to drive and own. And it will have plenty of personality and character.
Instead of me babbling on about a car I don't own, check out
www.saabnet.com and read the 9-3 Bulletin Board. If you search the 9-3 board for "audi" or "a6" you'll probably find posts about comparing both cars. Good luck with your shopping, both are great cars.