Warning: Contains spoilers for The Vampire Slayer #2
The Buffy the Vampire Slayer comic series The Vampire Slayer reveals a dark truth that proves Buffy Summers will always be the greatest Slayer, even if others take up the mantle. Being a Slayer in the Buffy universe means being chosen for a higher duty: killing monsters and protecting humanity from the forces of evil. However, the job comes with a heavy burden of death, suffering, and sacrifice.
The Buffy The Vampire Slayer TV show introduced the concept that for every generation there must be a Slayer, a human female who is chosen by fate to receive mystical powers from an ancient demon and fight the forces of evil. The series slowly expanded on this mythos, showing how there are actually many "Potentials" Slayers in the world, but only one is "activated" at any given time, the others acting as replacements in case of the (usually violent) death of the current Slayer. There have been exceptions to this rule, and multiple activated Slayers can operate at the same time. Also, the expansion of the Buffy franchise into its own Multiverse, the "Slayerverse," has created new Slayers from old characters, such as Fred and Willow, but being "chosen" does not necessarily means having what it takes for the job.
In The Vampire Slayer, a new comic book series by BOOM! Studios set in an alternate universe, Buffy has been inadvertently stripped of her powers and her memories by a spell from Willow, who has absorbed them and is now the Slayer. The spell was meant to alleviate Buffy's suffering by healing her from all the trauma she was experiencing as a Slayer, which was slowly breaking her. In The Vampire Slayer #2 by Sarah Gailey, Sonia Liao, and Valentina Pinto, the newly awakened Potential, Faith, explains to Willow and Giles why the spell went wrong. Trauma is, essentially, what being a Slayer is all about. By taking that away, Willow and Giles erased what made Buffy the person she is, basically killing her Slayer self.
Since its beginning, Buffy The Vampire Slayer has been about dealing with suffering and the dark side of expectations and duty, a big metaphor for the coming of age process. No matter how many Slayers there are, Buffy will always be the best because she is the one who is able to cope best with death and every other awful thing that comes with the job. This dark, ugly side is what broke Faith when she was introduced in the TV show, and it's breaking Willow in this comic series. This issue shows how important it is to live through trauma and to learn to cope with it. Willow just got Buffy's memories without the actual experience and she can't handle them, being tormented by images and thoughts of death.
Throughout the TV show and the follow-up comics, Buffy goes through an unbearable amount of suffering and sacrifice, but she endures it all, not because it is her "duty" as a Slayer, but for the sake of her friends and loved ones. In the end, being a Slayer is indeed about trauma, but what to do with that trauma and how to deal with it are the important things. Buffy, in all of her versions, embraces this dark truth behind her role, and this is why she will always be the greatest Slayer in any world.