Best oil SAE Paper 981443
SAE Paper 981443 describes experience from over 2.5 million miles of field trials and dynamometer tests with different MB engines during the development of the Flexible Service System. Analysis was made for Police, Taxi, and "Normal" use.
Although the oil brands used were not specified, the five authors, in addition to the three MB engineers, included two from Shell.
The objective was to determine the aging of the lubricants as related to vehicle use. I'm a two finger typist and it is not easy to type a long analysis of this paper, nor do I want to violate any copyrights, but I will say this, after reading this paper, anyone using a reasonable quality oil who is not operating a taxi or police car, should not find it necessary to change oil more frequently than MB recommends in the owner's manual, unless they enjoy doing it.
Since I also enjoy working on my cars, I change the oil about every 6000 miles(w/o filter change), about half way between the recommended mileage/time shown on the FSS, but I don't feel guilty if I miss a change for some reason.