Well I can't say much about Audis and BMW's but I have to say my dream car is the Viper Venom 650.
0-60mph (0-100km/h for you european guys) in 3.2
Top Speed 215 mph
All Street Legal, no turbos, no NOS and still out corners everything on the market except for maybe a Porsche 911 turbo, where I beleive its almost dead even