Two Convertibles with some similarities, but otherwise different in most aspects such as the modifications, horsepower, height, fuel economy, ground shadow size, and maximum occupancy. First of all, the 2018 Mercedes-Benz C-Class Convertible AMG C 43 has bigger and thirstier engine; the 2018 Alfa Romeo 4C Spider gets 6 more mpg. Also, the 2018 4C Spider is both slightly smaller and significantly shorter than the 2018 C-Class Convertible AMG C 43. In addition, you'll seat two more passengers in the C-Class Convertible AMG C 43 than in the 4C Spider. Among similarities are the body structure, market segment, and starting price.