It only allowed me to choose one, unfortunately. 

I think it's a website thing, as I just came across an older poll that had the same issue.

Again, I'd liked to have picked multiples and avoided the appearance of favouritism, but only the one choice was allowed.  "DDWtD" still remains the go-to work as far as compelling motivations for stopping the bad guys are concerned (no "They're holding up the cigarette delivery truck at the town border!  There'll be dozens of people demanding nicorette patches down at the pharmacy!  It'll be...well, not absolute chaos, but definitely crowded at the check-out counter!"), a villain base that offers multiple opportunities for both improv devices and obstacles, and villains that encompassed a wide range of powers, characterizations and fighting styles.  Mr. Willingham is to be congratulated on his crafting a work that has withstood the passage of a generation and is still as compelling as ever.

That stated, any number of the stories given on the above list could fit the same criteria.  Looking forward to more chances to give praise to all these works.