The best year is probably 1983. If I recall correctly, Mercedes Benz added some tighter emissions controls on the 1984 and 1985 models, more so on the 1985 because of the notorious trap oxidizer.

Keep in mind that the post-1983 models have better front and rear seat contouring, better front dome light, more rear knee-room, nicer door frame molding, (the felt one, that goes around the body of the car), velour weave carpet, and the 120mph speedometer. The seatbelts were easier to buckle too.

1982 models still had the "old" stuff.