Compare the BMW 4 Series M4 Cabriolet F83 - [2014] vs Mercedes A Class 45 AMG 2.0 Turbo - [2013]. 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 BMW 4 Series M4 Cabriolet F83 or the Mercedes A Class 45 AMG 2.0 Turbo. We'll leave it up to you to decide which is your favourite.