Originally Posted by ah-kay

1) If you like W123 then stay with them.
2) W124 1987 300D
3) W126 1986-1987 300SDL
4) W124 1990-1993 2.5L 300D
5) W201 probably all model years.

I would not care much about the other diesels. New diesels have too many electronic and is nothing but trouble. The list above is easy to DIY and have above average reliability. The bottom line, "Best" is relative plus how deep is your pocket to make it "Best".