Perhaps, at that time I may not have been able to properly gauge W126 State-side, but as a luxury car, it was relatively ubiquitous and something my dad's peers certainly aspired to own. Especially, as the competition was also nowhere near as crowded post-Lexus's intro of the LS400, essentially an homage of the W126.
For me, it's a toss up between the W140 and the W220...
The W140 was just the car. It was sleek and aerodynamic but the presence was only second to a Rolls-Royce. It was overbuilt and had so many features. Lexus and BMW responded in kind with the 3rd gen LS and E65/66 7er, respectively. The W220 was ironically a response to the Lexus LS and were so relatively common. Their higher-end S55 AMG cars set the tone for the horsepower wars that followed. Granted, build quality for a Merc took a nosedive.