I have just come to this thread and discovered that it was a good one until one person came along and messed it all up, you know who I'm talking about.
Now I'm trying to give you my general point of view on Audi vs. BMW:
First I must say I don't particularly like the both of the companies, but I don't hate them. Nevertheless I'd say I like Audi a little bit more, don't ask me why.
When it comes to driving I think the BMWs are more fun, and the Audis rather "play it safe". BMW has always sticked to RWD which makes them good drifters, usually connected to fun. The Audis, having AWD or FWD still can be quick on the track, but you know they were not build to be living on edge. On the other hand you can drive them much easier and won't sweat out a gallon of water when you're going quick.
I don't like Chris Bangles' design, but still I like the new M5, especially for it's engine. I liked some older BMWs though, like the M Coupe and the current M3. In my eyes Audis always look pretty boring, except of the TT. But that's another car I had get used to when looking at it. The ones I like are the RS4 and RS6.
Enginewise BMW has made some turbos, but today they're more into high-revving NA-engines. They're famous for their inline 6-cylinder for example. Audi likes to put in a turbo and also is successful with it, you do find the famous 1,8l turbo in a lot of different cars.
Both companies do have excellent build quality and the prices are not really different on comparable models, although pretty high in general. But you do get something for your money.
Conclusion:
I can't pull a clear winner out of the hat, because they both have advantages and disadvantages. When it comes to fun I think you're better off with a BMW. For a quick and easy traveller you better take an Audi.
Cheers,
the Interceptor