The best ever from what standpoint?

If you posed the question, if you have to drive one luxury sedan for the rest of your life, I would choose the 1989-1991 300SEL. Reliable, as comfortable as any other car, reasonably fast, and relatively simple.

Otherwise, the options are endless.

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!