Compare the Mercedes SL Class 63 AMG Cabriolet - [2017] vs Lamborghini Countach LP400 - [1974]. Find out which car is the fastest, most powerful, lightest or has the biggest engine in our top trumps style comparison page. Find out which car has the highest top speed or is the fastest accelerating, is it the Mercedes SL Class 63 AMG Cabriolet or the Lamborghini Countach LP400. We'll leave it up to you to decide which is your favourite.