Here are some links that might help with oil choices - look foroils with "MB Approval" designation and that correspond to your engine. Check with your MB service representative and always consult your vehicle's handbook - there's no substitute for RTFM.
My A class came with a complimentary litre of Shell Ultra - diesel, not sure if this was courtesy of the dealer or MB - probably MB! So will use that. My previous C class last service had Shell oil rather than Mobil so perhaps MB have changed preferred supplier? Incidentally in first 2000 miles my A class does not appear to have used any oil, which is good I guess, but previous two C classes used a litre of oil in the first 1000 miles, then very little between services.