Mum's car very recently developed creaking noises when driving over rough surfaces. I narrowed it down to the window seals as the noises would disappear when the windows were wound down and I have been through this on a BMW, Audi and VW. In all those cases the dealerships just kept on lubricating the seals. Mercedes however has confirmed they are replacing all of the seals.
Other than this issue this car has been pretty faultless to date in 2 years of ownership, which is nice especially considering my reservations regarding the solidity or certain parts of the interior.
My BMW 340i which is now just over 1.5years old has had the following issues:
1. Transmission failure leaving my then 6-8 month old son and wife stranded 3 hours from home. Put down to a 'software issue'.
2. A rear light fitting falling off. Put down to a known manufacturing defect and BMW ended up replacing both rear lights.
3. A faulty spark plug leading to rough running and left us in some sort of 'limp mode' on at least 3 occasions. It took them 3 attempts to diagnose this issue.
That said if the two cars are both sitting on the driveway I would grab the BMW keys every time. The turbo inline 6 rocks my world in a way a no 4 cylinder could ever hope to do.