I had to think about this one for a minute. (Way to go John - you little devil you! )
In this order, 1956, 1955, 1954. The '54 is, no doubt, lesser seen. Many people may confuse the '55 with the '56 but the '56 has come full cycle. In '54 the DeSoto was similar to other cars, not as distinctive as later year models. The '55 flirted with color breaks and started to sprout fins, albeit a little sheepishly. By fifty-six the car started to take on its own persona. The fins were developed and the car began to stand alone on its own merits.
55 gets my vote but all three are nice. To me the 54 just a bit awkward compare to other 54 marques maybe because it is seldom seen; the 56 fins are beginning to approach too much. . 😎✌️
The '54 for me. It's the grill that makes it my favorite. Followed by the '56 because I love the stacked bulb taillights. And then, the '55, again the grill is what pops it. As a side note, the dashboards on the '55 and '56 were outstanding to stare at.
LOL, we're opposites. It was the "teeth" in the grill that popped for me on the DeSoto's. I was disappointed when they were eliminated in '56. They had become sort of a DeSoto trademark.