The best thing to do is to follow your owners manuals.
When my ISP comes back up (their server went down this weakened), I have a page that shows some comparisons and also what the numbers mean. It is at
All oils will be good at the operating temp of all engines. the difference is different viscosity (therefore different protection) at a high temp and different rates of evaporation.
To me, the best viscosity for MB and BMW are either 0W-40 or 5W-40 but they are not easy to find. 10W-40 is also good but only a few synthetic oils at that viscosity are available.
In Germany, the only available Mobil 1 oils are:
0W-40 Turbo Diesel