You won't find many fans of the interior in the first-gen CTS. The current car's interior is MUCH nicer. And IMHO the upcoming 2010 LaCrosse might have the best interior yet in a GM car, and certainly the best yet in a Buick.
Clearly, expectations and evaluations of ride quality will vary. What you're used to will make a big difference. I have a Mazda Protege5 that has a fairly harsh ride. Then I test drove a Lotus Elise. After driving the Lotus, the Mazda felt like a Lincoln Navigator.
In general, if you care much more about ride quality than appearance or handling, you want the smallest wheels offered.