I've just been through this and bought a 2.0l TFSI petrol, manual A6 with leather. It's a 2010 with 62,000 miles on the clock. A couple of things about it are that firstly, I 'fall in love' with cars. It's ridiculous, I know, but that's how it is and this is a car I really wanted to buy.
I only have one recommendation which is unlike some other manufacturers, if they have a FASH, you can call Audi customer services to find out the entirety of the service history which is exactly what I did. The vehicle I bought only had one service from a non-Audi dealer and Audi gave me a complete list of everything that had been done to it. This included a cambelt change which was interesting as this was not included in the paperwork!
Finally, if you come across a 2.0l petrol, TFSI, 2008 - 2010 model, they are almost the same price as a, for example, 2006 model. What's the catch? Well, there is a risk because at the time, Audi had very expensive issues with the piston rings on this type of engine. However, I called Audi and asked them directly if any of the A6s were affected and they claimed only the A4s, A5s and Q5s were affected. My local dealer also told me this was the case but I found one BPJ-prefixed engine which was and it is still a risk that in a few months, I will have a big bill. I'm prepared to take that risk because of the price but it's something to watch for.