I can feel a flame war!!
I think the best thing for you to use would be Mobil 1, synthetic. You should do a search on this. There have been MANY topics covering this. You will learn a lot of valuable information and be able to decide for yourself which oil is best for you.
What kind of climate are you in? I use 20W 50, but it never goes below 40 F here! If it goes below 23 F, then you should use something lower than 20W. Good luck and don't forget the search!
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)