You havent said how far you drive, so i will assume its a long distance each year to justify the reliability risk, and lack of refinement that diesels suffer from. The Audi doesnt ride well and has very limited room in the back for something so big outside. However its either front or 4 wheel drive so at least it will work in the winter. The others are all rear drive, so if you live anywhere it often snows be prepared not to drive for a few days each year.

All have a few reliability issues, especially in diesel form (German cars arent as good as many people assume, but neither are they awful), and you havent said what engine you are after. A 6 cylinder version of all of these will be much nicer to drive, but use a little more fuel, and have a bit more to go wrong. But if you want a diesel coupe you dont have much choice.

Generally 6-cylinder diesels are more refined than 4-cylinder: but some of the newer fours are much better than older ones, especially from inside. Avoid a four-cylinder Mercedes diesel if you are after refinement.