Mercedes has long had a partnership with Mobil, and their factory fill synthetic is Mobil 1. Way back when I raced air cooled four strokes, dino oil would turn to sludge in no time, with cylinder head temps of 330F. We used Mobil 1 (in 1982 it was EXPENSIVE) and saved engines. They make some really good oils.
And I might buy it except for the price. Being able to buy a top tier synthetic for ~$8/L is amazing. So, Amsoil gets my business.
Oh, and rr's right, their filters ROCK.