Like advanced trigonometry, Buffy Math -- that is, math inspired by the TV show Buffy the Vampire Slayer -- should generally not be attempted outside of an AP high school class. It can be pretty difficult if you don't have a solid teacher guiding you through it, but some theories are worth exploring for extra credit. The Buffy Math on this one is relatively simple: Star Wars' Darth Maul is better than Darth Vader because Buffy's Spike is better than Angel. Yet, for some fans of both series, this one is going to be hard to believe.
Darth Vader has long been one of the most popular characters in Star Wars. From the moment he stormed onto the Blockade Runner in A New Hope, fans knew they were looking at something special. For many, the same was true when Darth Maul appeared in The Phantom Menace. The big difference was Vader's legend continued to grow throughout the original trilogy while Maul was sacrificed to the plot of a movie that was mediocre at best.
Then, the animated series Star Wars: The Clone Wars came along. Throughout the show, Maul was brought back from what turned out to be an exile of sorts, and tried to return himself to his former glory. The series Star Wars: Rebels took things a step further, depicting Maul on a strange path to pull redemption from his failures. He was still devoted to the Dark Side, but he seemed to be attempting to do good in his own twisted way.
Vader also took an infamous swing at redemption at the end of Return of the Jedi, though he was doing it to save his son. It was a spur of the moment decision that was unexpected to everyone involved, including Vader. Maul's mission to save himself was much longer and far more intentional than Vader's. He knew he had many mistakes to correct, most of which stemmed from his original mistake: trusting Palpatine.
This is where the Buffy Math comes in. Redemption was a key component of the stories of the vampires Spike and Angel, too. Both characters found it during Buffy the Vampire Slayer, but while they were on similar paths, one was certainly more rocky than the others'. Angel had redemption handed to him when his soul was restored through a gypsy curse. In contrast, Spike made the active decision to make himself better and earn his soul back, and ultimately sacrificed himself doing what was right.
So, the reason Spike and Maul could be considered greater than their franchise counterparts is that the path fought for is more valuable than the path handed to you. Both Angel and Vader's moments of redemption were handed to them, without either requesting them or seeking them out. On the other hand, Maul and Spike made the active choice to better themselves in their own unique ways. As such, their respective journeys are more compelling for the viewer and more valuable to the characters.
If Angel hadn't been cursed with his soul, he would have continued killing until a Slayer finally put him down. In fact, Buffy showed what happened to Angel when his soul was once again removed and he returned to being the killing machine known as Angelus. He only became Angel again after once more having his soul forced on him, and by that time Angelus had committed several horrific acts. Angelus never wanted to be Angel.
Vader's redemptive moment was by his choice, but it was a selfish one. Luke claimed there was conflict inside Vader, though there was little outward evidence of that in the original Star Wars trilogy. Vader's only real moment of conflict comes when the Emperor attacked Luke in the throne room on the Death Star II. Had it not been Luke specifically who was in danger, it's unlikely Vader would have turned on the Emperor at all. After all, he seemed pretty okay with hundreds of Rebel lives being lost in a nearby space battle.
Both Spike and Maul chose paths that were more difficult and time consuming than their compatriots. Despite still being a soulless vampire, Spike eventually found it in himself to do good, keeping in mind he had help and still did some awful stuff along the way. Maul's road to redemption was less about playing the hero and more about becoming a galactic crime lord, but he also sought to defeat the Emperor. In a way, he was doing good by doing bad.
Despite their bad choices, both Spike and Maul found a deeper, more profound level of redemption than Angel and Vader did. However, the perception of each property's fandom often seems to be the opposite. While he has his fans, Maul has never achieved the popularity or cultural notoriety of Vader. But that's what happens when one character's first appearance was in one of the most beloved movies of all time while the other first appeared in one of the most maligned.