Compare the Mercedes SL Class 300SL Gullwing W198 - [1955] vs Audi A7 3.0 TDI Sportback Competition Quattro - [2014]. 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 300SL Gullwing W198 or the Audi A7 3.0 TDI Sportback Competition Quattro. We'll leave it up to you to decide which is your favourite.