Mercedes-Benz CLK 55 AMG
Overall: I honestly wouldn't recommend buying this car to anyone, especially since you'll find more interesting cars in the D class. CLK 55 is very unstable while going through most of the corners. If you want to have to this car at all costs, consider buying a DTM version.
Mercedes-Benz CLK DTM AMG
Overall: This is a much better choice than the standard AMG version of Mercedes CLK, however you will also be able to find better cars in the B group. The most important thing is that you will be able to control it without any major problems.
Mercedes-Benz CLS 55 AMG
Overall: I wouldn't recommend buying this car unless you want to have a beautiful limousine at your disposal. I have to warn you, though. This vehicle is going to be much slower than most of the coupe cars from the D group, including Maserati GranSport and Aston Martin V8 Vantage.
Mercedes-Benz SLR McLaren
Overall: This is a very interesting choice, however you would be able to find better sports cars in the A group. Nevertheless, you shouldn't ignore this one right away. Go ahead and choose a test drive feature. SLR handles pretty well. It also has great braking system.
Mercedes-Benz SLK 55 AMG
Overall: It's a funny little car. It's slower than most of the D class vehicles, especially when it comes to maximum speed. Thankfully, you won't have any problems driving it, so if you're not experienced enough with faster cars, you may consider purchasing this one.
Mercedes-Benz SL 65 AMG
Overall: I honestly can't say anything good about this car. First of all, SL 65 is quite slow, especially if you take a closer look at the maximum speed bar (there's a well-known 250 km/h limit here). Driving it is also quite difficult and you will have to spend more 225000$ (+tuning).
Mercedes-Benz 300 SL Gullwing
Dealership: EUROPEAN CLASSIC
Overall: This is one of the classical vehicles of the game, so I guess you won't be surprised to see it in the G class. Sadly, you won't be able to win any tougher races in Gullwing, mostly because it's very slow. It's also unstable while taking corners. This is a car for collectors only!