KDI-18 "Imperial"
A good MOL model, the KDC-18 "Custom" and KDS-18 "Supurba" were BOL and TOL respectively.
Many here consider the 18 series to be the best KitchenAid dishwasher made and perhaps the best household dishwasher ever made. The 18s had "constant-rinse" which is the mini sprayer at the top that showers the tops of cups. 18s were also the first with a top spray arm, the 17s only had the bottom one. The 19 series energy saving models lost heated dry therefore they aren't highly sought after like 18s. I personally own a KDS-20, just like an 18, just no constant rinse.