Verified answer

Double check your information. The S500 was only produced up until the 2006 model year. As of 2007, with the introduction of the W221 chassis, it became the S550.

As for the 2 vehicles you're looking at, no one here can tell you which is the better buy. You would need to have both vehicles physically inspected by a dealer or other trusted shop to tell you the condition of each vehicle and decide for yourself after that.

you have not provided anywhere near enough information. If the desire is to buy cheap, buy the cheap one. If the desire is to get the best deal then YOU need to do some legwork and compare the options list, maintenance record, general condition of each, and lastly have both reviewed by a trusted mechanic.