My favourite is the 1987 E300D. If you can find a low mileage one
in good shape you will be lucky. Most I've seen on the internet have more than 150,000 miles, but are priced very reasonalby considering what a great car you get. If maintenance/repairs are not an issue to you I'd go that route. I recently had a '95 E300D that I had bought new and put 135,000 relatively troublefree miles on before selling it. It was a great car too. The some of the major differences, other than age is that the '95 has no turbo, has a R134 Climate control, smaller leather steering wheel, equally bad sounding yet worse looking audiosystem, no glove box, has a passenger airbag, has newer style alloy wheels, two aux cooling fans, and a much larger fuel tank, allowing a 700 mile cruising range, as well as newer style lower body cladding. There are other differences too, only less apparrent. Oh, the headlights on the 95 are an improvement over the 87.
The diesels between the 87 and the 95 had five-cylinder engines,
which some people prefer, but with which I have no experience.
Many of the members prefer the w123 diesels for their longevity
and classic Mercedes-Benz style, and their more DIY friendliness but sadly I've never had one of those either.
Hope this helps. Steve