Diesel or gasoline/ambitiousness or ambience????

Hello, maybe one of you can give me a decision help. I fluctuate when buying my A3 between nem 2.0 TDI and nem 2.0 petrol. The average driving performance will be about 15,000 km per year. Mostly city traffic with relatively short distances. Is there, also with regard to the fuel prices, the purchase of a TDI? Or because of the maintenance less. Furthermore, I had already set myself on the execution ambition. Unfortunately I had to read here in the forum That on bumpy routes or motorways the chassis is supposed to be an impediment. Does any of you have a 2007 ambition and can report something about the chassis? Maybe Audi has improved a bit. Most of the posts regarding the chassis were from 2003/2004. Thank you. Greetings