I misunderstood the question. Edit:
1. Mercedes CLS
The design may have some controversary, but the overall shape is the best. It is even better than the previous one, because the previous one had dropping lines front and back, by looking at the shape only you couldn't tell where is the front or the rear of the car. It looked coupé-like just because it was very sleek. The new CLS is now very nice, slight more uprigth rear window with slight longer bootlid would make the shape almost perfect.
2. BMW 6 Series GranCoupé
The 6 Series GranCoupé is too sedanish, but that is because it is based on the 6 Series Coupé, which afterall is a 2 door 5 Series Sedan. For that reason the lines are also the same. A design completly different than the 5 Series Sedan and 6 Series Coupé, just like the 5 Sereis GranTourismo is very different compared to the 5 Series Sedan, but based on the same rear shape the 6GC now has would make it really nice. But the side window of the rear door would have the be shorter, it goes too deep into the C pillar. Then the front hood is too long in proportion to the distance from the beginning of the front door to the rear of the car. In fact the front overhang is too long.
3. Jaguar XJ
Overhangs are short, high shoulder line, everything looks almost right. But the black C pillar gives it an interruption. It should have been in body color. But rear boot is also a bit high, something like Alfa 155, of course not to that extent.
4. Aston Martin Rapide
The rear shape is just like the DB9, coupé like. But with the added door, it make the rear to heavy. The C pillar is too thick, it should have been shortend by a slightly longer and going bootlid.
4. VW CC
Rear shape is an improvement over the Audi A7/A5 Sportback. But overall shape is not that good because of FWD chassis basis.
5. Audi A5/A7 Sportback
There is potential but it still has nothing coupé like. A5 Coupé with two added doors would be the right shape. The A7 rear is even worse, the rear drops way to much. All in all the Sportbacks don't really look coupé like, but rather Audi 100 Avant, so coupish wagons and not sedans.
6. Porsche Panamera
It can't be called a 4 door coupé and in the same time it could be the only car to be one. The Pany has right proportions, it is just unusual. Overall shape is more like a huge, but not high, BMW 1 Series Hatch. The Pany is more a 4 door GT, a bit like the FF that has only two doors. It is "like it" or "hate it". Just as it is placed on last place, it could be placed first, it is just a question of what to understand by "4 door coupé". A different car or a sporty low sedan without window frames?
