One of the biggest, heaviest, safest, most comfortable cars ever made. Longer, heavier, more fuel capacity, etc than the next body style in 2000, the W140 body M-B's were, and still are, some of the best road cars ever made. If you drive long, fairly straight and for long distances, this is the car for you. On the highway I get 20-22 mpg, same as the highway MPG for the 2007 Toyota's, so how can you go wrong. This car will make you feel you should be riding in back, not driving it.
Ultimate stability and road handling, Quiet; there is no road noise, no engine noise, no tire noise, nothing unless you turn on the radio or 6 CD changer.
The 4.3 L in the 400 can be a bit light, if you want to push it, but the 500 and 600 really drink the gas, so it is up to you.