Now, I have to say that I am in no way a hundred percent confident in this scale. For instance, Kahn may be before Ultron, and Darth Maul may be better than the White Witch. This is just a thought experiment to try to learn what kinds of villains are the best and I would encourage everyone who is interested in telling stories to do this experiment for themselves. The process can really help you realize what you think makes a good villain.
The second thing I wanted to mention before going on is that this is by no means an exhaustive list. It is just a list of the villains that came to the top of my head.
So, how did I actually figure out where different villains stand on my villain scale? Well, I actually tried not to overthink it. In general I went with my gut instinct, ranking each villain as either greater than or less than the last villain I had added to my scale. The end result is what you see above. For each character, the question I asked myself was:
How threatened did I feel by this villain?
This is important, because in lots of stories villains are threatening to the heroes, but we don't get it. They just don't seem scary or threatening. The reason for this reaction is that some of these villains haven't done anything within the story to make us believe that they are truly a threat. Being powerful isn't enough. We need to see something that we can point to and know beyond a shadow of a doubt: "That guy is bad. He or she has forsaken all goodness and humanity."
Later on in this post I want to touch specifically on a few villains to help give some justifiable evidence for how I have placed them on the scale. Before I do that however, I want to bring up two aspects that I think are critical for evaluating villains: Their motivation, and their key traits. Attention to these two things or lack thereof is what I think can make a villain either super original, or super cliche.
I've separated each of these two key aspects into three broad categories. Let's start with motivation:
In regards the the motivation of villains, I think that there are really only three things that drive villains to do what they do. Those are: Genuine conviction, cruelty and evil for cruelty and evil\'s sake, and lust for power. Clearly, the most common villain is motivated by lust for power. Far fewer villains are motivated by conviction or cruelty, and I think villains who are motivated by those things are more interesting for it. Now, just because a villain is interesting doesn't put him on the top of the villain scale, but it does help.
Now, on to key traits of villains:
Similar to how I think the most average villain is motivated by lust for power, I think the most average villain's key trait is simply being powerful. The most cliche villain then would be both power hungry and powerful. It follows then that some of the best villains would be a mixture of other motivations and traits. For the most part, I think that this evaluation indicates that the poorest villains are power hungry and powerful. Darth Vader, however, is an example of a villain who fits my cliche standard but who I ranked very high on the list. So there can clearly be exceptions and I intend to talk about some of them as I begin analyzing some of these characters individually.
Let's talk about the highest villain on my list first: The Joker. This guy's motivation and key trait are what make him so fearsome. He is completely mad, and he does what he does simply because he enjoys doing it. He doesn't want to rule the world, or become rich. This makes him threatening because there is no reasoning with him, no bribing him, and he has absolutely no reverence for life. His mercilessness was brutally established in the first scene as he killed all of his cronies. He is a freak with no conscience who wants nothing but to see people suffer.
Now it's time to talk about one of the most recognized and classic villains ever, Darth Vader, along with his grandson Kylo Ren. I'm considering these two together because they are undeniably similar. Both of these villains radiate an aura of power and strength. They carry themselves proudly and wield supernatural powers with ease, familiarity and comfort. The first time you are introduced to both of these characters they very quickly demonstrate their strength and willingness to destroy life. In one of his first moments, Vader is seen menacingly choking Captain Antilles and lifting him off the ground with one hand. Similarly, in his first scene, Kylo Ren kills Lor San Tekka and proceeds to suspend a laser blast in midair with the Force. These actions give us a footing, showing us that these are not guys you want to mess around with.
Now, though it gives both of these villains a good start, I don't think that this immediate show of power is necessarily the most essential explanation for why they are strong antagonists. I think key to these villains is who they kill. In a New Hope Vader kills his old master Obi-Wan. In the Force Awakens, Kylo kills his father Han Solo. By doing this, both villains demonstrate that they have forsaken all compassion and all love. They are completely devoted to their evil causes. We are convinced of this not because someone within the story told us, but because Vader and Ren's actions demonstrate it. These are those moments we can point to and say: "That is how I know Kylo Ren and Darth Vader are bad guys." Actions definitely speak louder than words as far as movie villains are concerned. 
I also wanted to address where I placed these characters on the motivation and key traits charts. Vader is obviously motivated lust for power, as are all Sith, but we are also shown in Revenge of the Sith that he has some level of conviction. Part of him believes that he restoring order to the galaxy. His key trait is obvious as well: he is powerful. He isn't uncannily crafty or insane, just powerful.
Turning to Kylo, I classified him as partly mad and partly powerful. This is because I believe that, while he doesn't have some mental defect, he is unhealthily obsessed with becoming as powerful as Darth Vader. That being said, I don't believe Kylo's principle motivation is lust for power. He truly believes that the dark side is right. He fears being tempted by the light side. As of yet, he has demonstrated no desire to rule the galaxy, only to live up to his grandfather's reputation. Part of me even thinks that Kylo Ren is a more fascinating character than Vader. Vader is more powerful, but 
Kylo is desperate which is more compelling.​​​​​​​
You may have noticed that Scar is only one cartoon villain made it onto my list. I'm sure there are other good cartoon villains, but Scar takes the cake in my opinion. Not only did he make my list, but he is featured third on that list. Why do you ask? Scar demonstrates his cruelty and scheming nature from the start. He will stop at nothing to become the king of Pride Rock. He kills Simba's father, Mufasa, and puts Simba in danger both with the hyenas and the herd of wildebeests. Then, as king he lets things go to ruin as he basks in his reign. Without a doubt, Scar is a villain who rivals even Darth Vader.
Speaking of scheming villains, it's now on to Loki and the new Lex Luthor. Why am I considering these two villains together? They are basically equal that's why. At least in my mind they are very similar. It's their brains that is threatening. They manipulate people and circumstances to get what they want. This places both of them under the scheming category for their character traits. However, though Lex is scheming, he is also slightly mad. He has some quirks (Jolly Ranchers and peach tea) which is why I classified him partly scheming, partly mad. Lex and Loki also have differing motivations. Lex doesn't seem to be power hungry, just set on pitting Batman and Superman. Loki on the other hand is one of the most power hungry villains around. In the end though, these two villains have basically the same impact on me. They are about the same threat level to me, and they are both middle of the road villains.
Alright, time to talk about Lord of the Rings. Here I want to compare Sauron, the primary villain of the series, to Gollum. Clearly, Sauron is "technically" the more threatening of the two characters, but I would argue that Gollum actually imposes his threat upon the audience more effectively. All the characters within the movie are afraid of Sauron's might, but no one ever interacts with him face to face the way Frodo and Sam interact with Gollum. In addition, Gollum has a sense of uncertainty that Sauron doesn't. We the viewers are always tense with anticipation, knowing that Gollum could turn on the hobbits at any second. Though Sauron commands armies and wields magic, it seems to me that he doesn't have the levels of intrigue that are found in Gollum.
Finally, I want to address a couple of the lower characters on my scale. I will specifically be looking at Darth Maul and that dark elf guy from Thor: The Dark World. (He was so boring to me that I didn't even take the effort to look up his name.) We are told that both of these characters are powerful and fearsome and both of them kill someone important. Darth Maul kills Qui-Gon, and the dark elf kills Thor's mom. So why are they boring? I think it is because they just kind of come and fight the good guys. They don't have layers or personalities.
All the elf guy did was command an army. He didn't have any personality or motive. At least Loki and Luthor had interesting personalities. Having an army doesn't create an interesting villain.
I personally think Darth Maul had a ton of potential, but he didn't pose a genuine threat to anybody until late in the third act of the Phantom Menace. (The five second duel on Tatooine doesn't count as threatening.) Maul is supposedly the namesake of the movie right? Yes, people say it could be Sidious or even Darth Jar-Jar, but Darth Maul is the only lead villain who shows his face. If we had seen him working in the shadows to disrupt the heroes' plans from the very beginning of the film, then the heroes would have known that someone is messing with them, but they wouldn't have known who until Tatooine. This would have added a layer of mystery and questions that wasn't there. Compare Maul with Vader or Kylo: both posed a threat throughout their entire film, and established  their strength and comfort with their powers early in the first act.
So, in conclusion, I think a strong villain should:
Have genuine motive
Have interesting personality
Have more to him than just a big army
Show me not tell me that that he is a threat
Thanks for reading everybody! I hope you enjoyed my thoughts on movie villains. Have a great day folks!