Well, all three cars have a special place in my heart.

The 300D for being the utilitarian car that it really is, for being smaller, lighter and more nimble. Pretty much the same way I feel about the 300TD, but you can haul more crap around with it. Bonus.

The 300SD for being a TANK. The ride, the feeling of being so safe and secure like driving a bank vault. The ride at high speed, seems like no speed phases this car, 100, 110, 120, 130.. (had my old 420SEL to 130, awsome). Handling is amazing to, IMHO, better than the 300D.

Bottom line, if you do alot of city driving, go for the 300D/TD. Highway driving, go for the SD.