Long before Bella made doe-eyes at Edward from across a science class desk, Buffy Summers was dating and slaying blood-sucking vampires while maintaining her GPA. Though the Twilight Saga films and Buffy the Vampire Slayer series share several thematic elements like teenage melodrama, vampires, and world-ending apocalypses, they couldn't be more different as franchises.
Their basic plot structures have led to some serious conflicts between the fanbases; where one focuses on a teenage girl who sacrifices her self-worth to devote herself to loving a vampire, the other emphasizes a teenage girl sacrificing vampires to devote her life to loving herself. It's possible to be fans of both, but the messages inherent in either inspire some rather competitive memes.
Dinner For Two
The majority of the action in the Twilight Saga revolves around Bella and Edward's romance, with the war between various vampire and werewolf factions born from their taboo love affair. Some viewers found many aspects of the pairs' courtship too maudlin to take seriously and wished for some more believable tension.
Had a Buffy/Twilight cross-over film been explored, some audiences might have found a reason to sit through Edward and Bella's dates. Buffy Summers, who wouldn't have tolerated most of the shenanigans involved with dating Edward, would have most likely saved Bella the trouble and staked him immediately.
Slayer Vs. Swan
Though Buffy had a tumultuous relationship with her vampire lovers Angel and Spike, she always made sure that they respected her boundaries. In the season two episode "Innocence," when Angel tried to discard Buffy after their first night of intimacy, she picked herself up and refused to be treated poorly because of his insecurities.
Bella by contrast put Edward on a pedestal to the point where her own insecurities were greatly amplified. In her eyes, he could do no wrong, no matter how manipulative his behavior was, and she was willing to do whatever it took to force their relationship to work, even if it meant sacrificing her independence.
Still A Better Love Story Than Twilight
Buffy and Angel's relationship wasn't perfect, and, in many ways, it was unhealthy, but one of the most mature things that came from it was Buffy and Angel realizing the best thing for them to do was not stay together.
Whenever Angel and Buffy were intimate, Angel risked losing his soul, and, when that happened, he became Angelus and initiated homicidal rampages. For the sake of Buffy and Sunnydale's safety, he had to stay away from her, and she from him. It took an admission of responsibility that Edward and Bella simply never had, no matter how unhealthy their relationship became.
Who Would Win?
Buffy has faced some pretty powerful vampires, from Count Dracula himself to The First, so taking out one sparkling high school student wouldn't be all that difficult. Even with his super strength and agility, his powers wouldn't be anything she hadn't faced before.
Even if Edward tried to seduce her, she wouldn't fall for his pretty-boy charms. After having dated both Angel and Spike, two powerful and dangerous creatures of the night, she most likely wouldn't be interested in his lack of personality.
Franchise Lessons
In the earliest episodes of Buffy the Vampire Slayer, even when it appeared that Buffy was too smitten over Angel to realize her own worth, she always found reasons to rely on her own agency and divorce her worth from having a man by her side.
Twilight, in contrast, instructs young women that their behaviors directly influence their male partners, to the point where they become responsible for their partners' outbursts, forcing them to change who they are in order to keep them.
Sparkle Vampire
In the Twilight books, Edward is described through Bella's eyes, and her perspective informs the reader about everything from his personality to his physical appearance. She often compares him to the Greek god Adonis, and describes his skin like marble; rock hard, very pale, cold as ice, and sparkly in the sunlight.
While vampires in other works of fiction have always been very pale and cool to the touch, they've never "sparkled"—they've also never gone out in the daylight—which makes Edward unique and easy to make fun by those that like their vampires to be blood-thirsty monsters.
Buffy Vs. Edward
If Edward's sparkling, perfect body and manipulative ways weren't contentious enough, he was also reportedly indestructible. Most vampires have some sort of weakness, whether it's holy water or a crossbow through the heart, so, making him unkillable drastically reduced the stakes of any of his actions.
In Buffy the Vampire Slayer, all vampires had some sort of flaw, like Dracula, who had to sleep in a coffin filled with dirt from Transylvania. Buffy found a way to kill every one of them, and it's not far-fetched to think that with help from the Scoobies she'd find a way to end Edward.
Girl Power
The 90s was the era of "grrl power" where characters like Buffy Summers and artists like Tori Amos were telling young women to kick ass and be independent without needing a man in their lives. Buffy showed her fans that they could be strong, fierce, and self-reliant.
The men in Buffy's life wanted to be with her because she was brave, resilient, and compassionate. She may not have needed saving, but she wanted someone to fight alongside her, which was a very different relationship dynamic than the one being pushed in the Twilight Saga.
Watch The Sparks Fly
Spike and Buffy's relationship was notable for having its roots in animosity whereby the Slayer gradually fell in love with her enemy, and he with her. Spike was a villain in his first appearance in the series, but he slowly became an anti-hero and the recipient of Buffy's begrudging respect.
They went from fighting against each other to fighting alongside each other, and their love matured depending on the crisis that they faced together. Appearing together in a Twilight film, and they'd completely upstage Edward and Bella, who were never able to complement each other's strengths.
How Twilight Should've Ended
To many viewers, the perfect ending to the Twilight Saga wasn't Bella and Edward living happily ever after with their half-human half-vampire spawn Renesmee, but Edward getting staked by Buffy on her way to rescue Bella from a horrible mistake.
If she'd succeeded, Bella wouldn't have almost died from having a mutant baby and learned from the Slayer how to respect herself and not put the desires of a man before her own happiness.