First off...I am not a Tech. The following is just my opinion based on looking at pictures of the 300SDL oilpan and dipstick tube.
Level ground is most likely your best bet because the dipstick tube goes to the deepest portion of the oilpan. Since the tube is on the right side of the car you might get a few extra drops by SLIGHTLY raising the left side of the car. You don't want to raise the back or front.
I'm sure the Techs here know better than I.