The Mercedes S-Class is easily the best car in its class, but it also shows up much more expensive models with its sublime ride, expansive tech package and luxurious interior. It’s supremely comfortable while still being good to drive, and the new straight-six diesel engine is more powerful, smoother and quieter than the previous V6. Even as the cheapest long-wheelbase model in the range, this new S 350 d retains its place at the top of the pile, and is a worthy flagship model for Mercedes.