Two Convertibles with some similarities, but otherwise different in most aspects such as the starting price, height, horsepower, fuel economy, ground shadow size, and maximum occupancy. First of all, the 2017 Audi A3 Convertible is priced $28,300 lower compared to the base MSRP of the 2018 Alfa Romeo 4C Spider. Also, the 2018 4C Spider has a more powerful engine than the 2017 A3 Convertible, but it gets 1.5 more miles on a gallon of fuel. In addition, the 4C Spider is both slightly smaller and significantly shorter than the A3 Convertible. And finally, you'll seat two more passengers in the Audi A3 Convertible than in the Alfa Romeo 4C Spider. Among similarities are the body structure and market segment.