Having own a 89 300E, and currently owning a 95 E420 and 94 E500, I would say the best overall value is my 95 E420.
When I sold my 300E and bought my E420 I was afraid of the gas mileage issue, going from a 6 to a 8, but that was never an issue. Truth be told I get the same gas mileage in both cars 300E & E420). The E500 is another story. That is a gas guzzling son of a b----!!!