Your car is probably FSS and needs MB 229.3 spec synthetic (group III and IV oils) for that feature. If you want to go with the traditional 5,000 mile changes, conventional oil will be OK.

The widely available 229.3 oils that I know of are Mobil1 0w-40, and Valvoline SynPower 5w-40.

FYI, I posted a used oil analysis of M1 0w-40, the sample taken during a Service A as indicated by FSS:
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=002477#000000