MIAMI — If somebody ever would give me $200,000 with the stipulation that I had to spend it all on my next car, at least I know now where I would start. I would head for the nearest Mercedes-Benz showroom and asked the first salesman to take me to the 2019 AMG S63 Coupe. I just might stop shopping there. Though there is no such thing as a “perfect” automobile, a designation that likely would vary from person to person, the S63 Coupe comes as close as any with high marks in performance, appearance, technological features, comfort, and prestige.