Mike's quote from Randy Durrance is spot on as is a quote from a gent out in Texas, Larry Bible, of "change it hot and often".
My particular favorite for all 3 of my gas vehicles is Chevron Delo 15W-40. I can find it at Walmart, reasonably priced and in gallon jugs. It came recommended to me and has been my favortie for several years. It has ratings for both diesel and gas.
But I wouldn't get hung up too much on brand as I would on oil change frequency and proper viscosity for the weather. Mercedes now appears to not list brands in their supplemental as much (if at all) as they list approved API service categories and the good old temperature vs viscosity chart.