You have such a wide range in cars there.. S2000 to an Audi A6! Completly different vehicles with different ideas.
You need to write down on paper what you need, what you want, what you can\'t live with out.
For me - I needed a four door, I wanted a sports car, and I could not live with out AWD.
So I looked, I had a 2000 Nissan Pathfinder for a year, but then I realized I wanted a car / sports car. So I looked at the Subaru 2.5RS, then the WRX, then the Audi A4.
I realized that most of my time was going to be spent comuting, so I leaned more toward the Audi. Then I test drove the 2.8, found a great deal on it and now thats what I have!!!!
So may I also suggest to your list the new Audi A4 - very nice car, refined interior, much nicer its BMW competitor. BMW makes a fine car mind you, just the Audis have always been a bit better on the inside. The Audi is also very tunable. But like I said, you need to figure out what your wants and needs are.