So, here I go again.

I hope, my translations are understandable...
Driving dynamics:
The handling of both cars facilitate safety and it also shows that safeness can be compared with "driving fun".
Especially the Audi is a pleasure to drive and he is fast in curves - although the engine is heavy and the front wheel drive). The steering is direct and smooth-running.
With deactivated ESP, the Audi has some problems with the traction, and then the Mercedes has room to play off his advantages.
The E 280 is fast and good-natured, but the Audi is still faster around the handling cours. The ESP of the Mercedes isn't that sensitive then the Audi ones and makes the E-Class more a cruiser.
The Audi also has the better brakes. The brakes of both cars are great to handle. Nevertheless the brakes of the Audi are in warm condition better, then the (also very good) brakes of the Mercedes.
running costs
It's extremely infrequent that the costs of two cars are that different. The price of the Mercedes is over 4000 € higher, then the starting price of the Audi.
For those, who want to resale their car, the Audi is also the better choice. The owner of an E 280 will loose more then 2000 € compared to the Audi owner (after 80000 km / 4 years).
Only the lower CO2 emission of the expensive Mercedes is better then the Audi ones. The A6 has lower running costs, otherwise.