Two Convertibles with some similarities, but otherwise different in most aspects such as the starting price, horsepower, fuel economy, ground shadow size, and height. First of all, the 2018 Alfa Romeo 4C Spider is priced $22,300 lower compared to the base MSRP of the 2018 Mercedes-Benz SL-Class. Also, the 2018 SL-Class has bigger and thirstier engine; the 2018 4C Spider gets 6.5 more mpg. And finally, the 4C Spider is both significantly smaller and slightly shorter than the SL-Class. Among similarities are the body structure, market segment, and maximum occupancy.