Understand that on any German car that if a drain plug has a washer, this washer is always replaced with a new one and never reused.
This car is designed to have motor oil "vacuumed" out the dipstick tube, and it's sure an easier process and removes the same amount of oil (or more) than draining.
It's the 21st century--why would you even consider nonsynthetic motor oil?
And forget completely all SMs and SJs and viscocity figures and look instead for Mercedes specification approval printed ON THE BOTTLE. Follow recommendations here:
http://www.startekinfo.com/StarTek/outside/9511/?requestedDocId=9511
Your best bet for motor oil is Mobil 1 European Formula 0W-40, which meets Mercedes specifications. Remember, if the Mercedes 229.x number is not printed on the bottle, the oil is NOT suitable for a Mercedes.