Both heroes and villains made a home in the small town of Mystic Falls. The heroes may have been the reason to begin the show in the first place, and seeing what happened to them was likely the reason to continue watching. But they weren't the only thing that kept the show interesting over the years.
The villains were also often tremendous. Eccentric, witty, and thinking ahead were the genuinely evil, maniacal, and brilliant antagonists. They didn't need to be likable. Instead, some thrived off of being as traditionally unlikable as possible. They were awful people willing to go above and beyond what was necessary to achieve their goals, yet they had a magnetism that could not be denied, and thus perhaps that made them the best part of the show.
Heroes: Emotional Plights Had More Substance
The villains definitely had depth and substance, but the focus on the heroes allowed them to have a bigger arc in dealing with their past and future. Plenty of Stefan's storyline involved his guilt toward convincing Damon to become a vampire and his actions as the Ripper.
Elena's fear of becoming a vampire and itting she has never wanted to transition after Damon feeds Elena his blood not only plays a role while preparing for Klaus' ritual, but it also appears later after Elena does die with vampire blood in her system.
Villains: Willingness To Go As Far As Possible
While the heroes tended to be faced with more questions regarding keeping their friends safe and finding ways to protect loved ones, the villains had no such things to worry about. As antagonists, they had the chance to push as far as they wanted to.
Klaus made that clear when he was nearing breaking his werewolf bind. Klaus ensured he would break the curse by having back-ups to each part that was necessary for the ritual. He even took advantage of Stefan's desperation to save Damon by getting him to Klaus in making hybrids and forcing Stefan to turn off his humanity.
Heroes: They Could Be Villains Too
There were times when The Vampire Diaries mixed things up by having their main characters be the villains. The first opponent to appear was Damon Salvatore, who eventually transformed into one of the show's heroes. However, there were still numerous times throughout his time in Mystic Falls that Damon was definitely the villain of the story, including nearly everything he does throughout the first season and his involvement with the sirens in the final episodes.
Stefan also played the role of the enemy. When his humanity was off while he worked for Klaus, Stefan was clearly one of the bad guys. Stefan became one of the antagonists or problems in Mystic Falls any time Ripper Stefan or no humanity Stefan came out.
Villains: More Exciting Than Protagonists
Even though the heroes can be unpredictable, the villains tend to be more exciting. They have charisma going for them in ways that make them entertaining. Kai, known for being one of the best villains, creates an environment that makes everyone else annoyed and frustrated to be around him. However, he is also a sociopath and is not afraid to harm others to reach his goal.
The Mikaelson siblings, mostly shown through the more chaotic Klaus and Kol, had ways of getting what they wanted for a bigger endgame or pure enjoyment.
Heroes: Main Characters
As fun as the enemies may have been to watch, they didn't tend to stick around for long. However, the main heroes were major presences for the entire series or most of it.
Given so many of them were around for so much longer than the villains, it allowed for more character arcs, substance, and emotional connections to those in Mystic Falls.
Villains: Forcing Twists And Turns
Damon spent his entire vampire life waiting to open the tomb and reunite with Katherine. Unfortunately, everything he did was in vain as Katherine was not in the tomb and had escaped in 1864, never bothering to reunite with Damon. Katherine faking her own death to escape Klaus was an intriguing element and it also changed Damon's perspective of Katherine forever.
Rebekah Mikaelson pulls off one of the biggest plot twists that changes everything. To save her family, Rebekah stands in the middle of the road on Wickery Bridge, gambling that Matt would swerve to avoid her. When he does, Matt drives the truck, with he and Elena inside, off Wickery Bridge into the water. Stefan rescuing Matt left Elena to die with Damon's blood in her system, putting Elena in transition. Killing Elena also put Rebekah at odds with Klaus since Elena as a vampire prevented Klaus from making more Hybrids.
Heroes: Stakes
Being emotionally invested in the heroes meant being more concerned about their lives. The group was constantly trying to keep themselves alive and Mystic Falls safe. There were several times where their opponent was older, more powerful, or smarter than them.
This meant that they were more likely to die compared to their enemy. Over the years, many of them did die, and some were lucky enough to return to life, while others found peace in the afterlife.
Villains: Often A Few Steps Ahead
Stefan and Damon had Katherine cornered and could have likely ended her life during "Masquerade" had Katherine not been a few steps ahead. Katherine linked herself to Elena, knowing Stefan and Damon wouldn't dare kill her if it meant Elena would die too. Katherine's scheme proved how well she knew the Salvatore brothers, and she got to leave the party with her life intact even if the linking spell had already been lifted.
Kai was also never shy about his intentions, and it was obvious that he was willing to do anything it took to escape the prison world as soon as he had the means. Since Kai knew more about the Prison World than Damon and Bonnie, he was often a few steps ahead of them. However, the real proof of Kai being ahead of the group came when he linked Bonnie and Elena. Kai understood the dynamics at play between everyone and made a linking spell as revenge.
Heroes: The Importance Of Humanity
There needed to be an anchor to what it meant to be human in a series filled with vampires. Matt Donovan filled that role for the entirety of the show. Matt was the only of his friends never to be personally involved in the supernatural world, even as all his friends became vampires, werewolves, and witches.
Throughout it all, Matt was devoted to staying human, growing up, and living his life. When he got older, he expanded beyond trying to keep himself human. He got involved in protecting the town from supernatural elements, wishing to keep the Mystic Falls residents safe and human.
Villains: Can Make Heroes Turn On Each Other
One of the most intriguing elements is how alliances, truces, deals, and manipulation can make the main characters turn against each other. Klaus's impact on Tyler's life pinned him against Caroline when she told Tyler he could pursue revenge or stay with her.
Katherine's existence created an antagonistic relationship between Stefan and Damon. Kol compelled Damon to kill Jeremy then acted as if the entire thing amused him. Kai used magic to convince Damon that Damon had hurt Kai when instead, Damon had hurt Elena.