I have owned both Mercedes and BMWs. Here is my two cents.
With respect the big models, Mercedes is by far the better car because they produce more cars.
I had a 1995 740 that needed a new engine at 60,000 miles. The aluminum alloy that was used in the engine blocks (that were not sleeved) was corroding. BMW quietly replaced the engine on many of those new V8s. I feel sorry for the guy that didn't complain.
Same car also had transmission replaced at about 70,000 miles.
And I baby my cars!
This is unheard of for Mercedes. The difference was the number of S class sold versus 7 series.
With all that said, the BMW 3 series, which is produced in high quantities, is a great automobile.
However, I will never buy another BMW V8 again.
1992 500 SL
2002 Mini Cooper
2003 Harley Electra Glide