Most if not all of the modern 2 part paint formulations are basically the same. The best of them depend upon a highly toxic isocyanate hardener that provides for a very shiny, hard, durable finish that allows it to be color (clear) sanded and then buffed to a highly smooth finish. The fact that it can be color sanded 24 hours after application allows the painter to remove many of the imperfections that you would just have to live with if using a synthetic or 1 part acrylic enamel finish as was the original paint on most MBs of the 113 era. Some special order MBs came with a lacquer finish that could be color sanded but this finish while used on show cars primarily because it could be buffed to a show qulaity finish did not use a hardener and thus was not as durable and was highly subject to cracking and crazing--especially if left outside subject to multiple heat cycles. Bottom line is that Dupont, Glasurit, PPG, Standox all produce a quality product. Individual painters have their favorites and I would agree that color match, surface prep and use of a complete single line of products from one manuafacturer (to ensure compatibility of successive coats) from primer, through primer surfacer and top coats is probably the most important thing to look for. Primarily out of availability considerations, I went with PPG acrylic urethane and I'm most pleased with the results--and I did the prep and paint work myself. For more info on paint, you may want to frequent Len Stuart's Autobody website--there is a wealth of paint info there.
George