BMW vs. Audi vs. Benz vs. Lexus vs. Infiniti is really a pointless argument at the end of the day.
You're buying a specific car, not the entire car line. Comparing the A4 vs. the 3-Series or the A6 vs. the 5-series is far more relevant, no? You can look at overall brand reliability, warranty, service, etc. but if Audi has a fantastic $500k supercar and BMW doesn't is irrelevant to pretty much everyone. It looks good on the cover of Car & Driver but that's about it. It has zero relevance to anything you're actually ever going to buy.
Car companies build super-expensive cars not to turn a profit but exactly because people see these cars and make assumptions about the brand overall (racing heritage, engineering prowess, etc.) and assume that influences the cars they can actually afford. If this marketing strategy didn't work they wouldn't do it.
You're way better off worrying about what specific car is best for you rather than make assumptions about a 328 or an A4 based on a $180k+ car with zero similarities except a nameplate.
For me it came down to reliability. Anecdotally speaking everyone I know who's owned an Audi, including recent ones has had issues with it. They drive nice and feel nice but in my mind they are among the least reliable brands out there. BMW's aren't exactly Hondas or Toyotas but in my experience they are more reliable than Audis.
Personally I would rather see both companies (along with Mercedes, Land rover & others) invest more in making more reliably cars than irrelevant cars that cost as much as a house and are pretty much marketing stunts. I would be much more impressed if BMW would spend engineering dollars on making my 1-series hold up more like a Lexus while still driving like a BMW. Now THAT would impress me.
2012 135 Convertible
2010 Lexus RX350