Supernatural's take on the supernatural is one of the main reasons why it has lasted so long. It takes itself seriously in its depiction of the other-worldly, resisting the urge to camp up featured monsters. Also, almost every creature Sam and Dean face are humanoid in appearance, meaning that a scary monster isn't ruined by bad special effects.
One of the best elements of the supernatural the series has managed to portray is demons. Although they appear human, their lack of a soul makes them one of the scariest creatures the Winchesters have faced. However, there have also been some demons who have managed to rub fans up the wrong way.
10 Worst - Cain
What with Cain being the Father of Murder and all, one would have expected him to be a lot more threatening than he appeared. However, that was not the case. When Cain was first introduced, sure his manners weren't up to much but aside from that, he was pretty tame.
Admittedly, his backstory helped to fill in the gaps and it did confirm that he had once been a terrifying demon, but because the audience didn't get to see just how awful and evil he was, it was difficult to buy.
9 Best - Abaddon
Although Abaddon's time on the show didn't last as long as other primary antagonists, she established herself as a force to be reckoned with. She first appeared in Season 8 in a one-off appearance and was captivating right from the start.
She took over the role of antagonist during Season 9, displacing Crowley as the King of Hell. Knowing how powerful Crowley was at that point, this was already an impressive feat. The great thing about this Knight of Hell was that she wasn't afraid to go for the jugular; during her time on Supernatural, she managed to successfully kill Sam and Dean's grandfather, Henry.
8 Worst - Ruby
When Ruby first appeared, she was a unique take on demonkind. She fought and killed other demons alongside the Winchesters, making herself a lot of formidable enemies in the process, including Lilith. Due to her demon status, Dean was particularly unwilling to trust her.
Sam, on the other hand, began to see her as an ally pretty quickly. This is partly due to his willingness to see the good in everyone, but Ruby was also training him to use his powers. This involved getting Sam addicted to demon blood, which caused a massive rift between the two brothers. In the end, Ruby revealed she had been working for Lucifer all along.
7 Best - The Seven Deadly Sins
Okay, technically these are seven different demons but because they all appear together as a group, we've collated them into one entry. The Sins's first and only appearance (so far) was way back in the premiere of Season 3, just after thousands of demons escaped from hell and on to earth.
Unlike regular demons, each one of the Sins had an ability to manipulate humans around them according to their individual sin. For example, Gluttony had the ability to force anyone to eat what he wanted, resulting in a scene that was equal measures harrowing and gross to watch.
6 Worst - Meg (In Her First Body)
The demon known as 'Meg' was another peculiar one. Initially, she started out as a total antagonist but later on in the series she became a sort of antihero, developing a weird but cute relationship with Castiel that lasted until her death in Season 8.
However, when Meg first appeared, she was more than a little annoying. She probably would have made a better villain if she hadn't basically been Azazel's lackey for the whole of the first season. It took away her status and reduced her threat level so eventually, Meg became a demon that the Winchesters could defeat with relative ease.
5 Best - Demon Dean
Back in its tenth season, Supernatural knew it had to give the audience something new to give them a reason to keep on coming back. This is when Demon Dean was born. After a long and exhausting battle with Metatron, Dean, unfortunately, lost his life. However, thanks to the Mark of Cain, he was resurrected as a demon.
Demon Dean was more rash than human Dean but thanks to his lack of a soul, he was also careless, selfish and did anything he wanted, regardless of the consequences. For the viewers though, it was just fun to watch Dean and Crowley buddy up together. However, the image of Dean hunting Sam in the bunker is still creepy to this day.
4 Worst - Lilith
Lilith was the main villain of Seasons 3 and 4 of Supernatural. During the former she proved herself to be a great antagonist, first by blowing up a whole load of the Winchester's allies and then by possessing a little girl in the season finale, which made everything she did that much more terrifying.
However, in the show's fourth season, Lilith lost her edge. Despite being one of the season's main antagonists, Lilith stuck to the shadows, never really making an appearance. She was also less fun as there was no more possessing children. Instead, she became obsessed with breaking the Seals and freeing Lucifer from his cage, which made for a fairly boring villain.
3 Best - Azazel
For a new series like Supernatural to establish itself as a show to watch, it has to have a great villain in the works from the off. Thankfully, it succeeded with its first primary antagonist, Azazel. Although Azazel didn't feature much in Season 1, his presence was constantly felt.
In the very first episode, he killed Sam's girlfriend Jessica and also killed the Winchesters' mother in the same way years ago. Azazel's endgame was also well thought out and made for a satisfying resolution of his arc. Additionally, Sam and Dean were obsessed with killing the demon for the first 2 seasons, launching Supernatural into mainstream culture.
2 Worst - Asmodeus
To be fair, Asmodeus had one hell of a job following in Crowley's footsteps as the new demon antagonist. Unfortunately, he failed. Sure, he achieved a couple of things during his short stint on the show, such as capturing and subsequently torturing Gabriel which was probably no mean feat (we're assuming).
However, Azmodeus's primary aim seemed to be to take over hell. While this is a noble goal for a demon, the whole new-King-of-Hell concept had been done countless times in the first 12 seasons. Ultimately, while he was on Supernatural, Azmodeus didn't particularly contribute to any of the season's overarching storylines.
1 Best - Crowley
Who else but Crowley could take this position? He was a smooth, sarcastic, evil, quick-witted demon who loved to cause chaos for the Winchesters whenever he popped up. He wasn't averse to helping them out, so long as there was something in it for him, but he didn't mind killing them if he needed to.
As a demon, Crowley has committed some truly terrible deeds in order to get what he wanted, including killing Kevin's best friend, befriending the Darkness and killing all of the people the Winchesters saved over the years to stop them from closing the Gates of Hell. However, he also struck up a weird friendship with them over time and became a much-loved character in his own right.