This argument has me thinking something else over: I think a case might exist that Superman has better willpower then Hal Jordan.
First off, Kal took Sinestro's ring, and casually captured Parallax with it. He also claimed he allowed himself to be taken over the first time, to save some people.
That already puts him up there with the best, considering his lack of experience with rings, and with entities (Kyle Rayner and Hal both fell hard their first time against Parallax's manipulations.)
Outlier? It is NOT.
ECLIPSO: The Darkness Within. Hal Jordan falls pretty easily to the black diamonds influence, lacking the will to curb his anger. Meanwhile, Superman grips a diamond in his hand, narrates what it feels like, and let's it go. ECLIPSO has to force him to MAKE himself angry, by threatening civilians, just as Parallax did.
So that's two examples.
Can anyone think of others? Wosuld Milton Fine Brainiac be applicable here, as one of the most powerful telepaths in comic book history, vs Hal's various performances? (Can Hal hold off an amped Hammond or Grodd by will alone, as Superman has Milton Fine?)