Agreed about the disappointing MPG numbers. Granted January has been pretty chilly, teens to mid 20's for day time highs. And I do live in an area where stop signs grow like weeds. When I'm back in Kansas/OK visiting relatives, being able to drive for miles without a stop sign or light is just great
If you're doing mostly highway driving, the A3 should shine. Looked at the 2010 Prius -- online, didn't drive it. I believe it's the better car for city commutes. From what I could tell in the specs, it has more tech stuff compared to the Audi. In the end, we really liked the handling, performance, and overall looks of the Audi. Like the DSG transmission. Had a 91 Mustang GT, and a 91 Acura Integra both manuals. That was fun, but in Chicago I'll stick with the auto.
Traded in a 99.5 Jetta VR6 for the A3. That was a love/hate car. When everything worked I loved the Jetta. The interior was nice but it's made of cheap plastic parts that broke when you used it. The Audi interior seems to be built better, the glove box was my test. It has a nice feel, and so far the hinges haven't given way to the cold -- unlike the Jetta! After the third glove box hinge broke I left it.
Ideally the Prius would be your city car, and the A3 is the highway car. But if you had to have just one, I'd get the A3!