Every Pokemon generation has done more than just introduce new Pokemon, it has also introduced new villains. While Team Rocket is known by all, there are nearly as many villain groups as there are generations. They all have different aesthetics, goals, and tend to use different types of Pokemon.
Not every villain group is as popular as the other. Some are near and dear to the Pokemon franchise while others are often forgotten by fans. The best of the villains are memorable and well written while the worst are forgettable with poor writing. Some are also just the best because they are simple and nostalgic.
S Tier
Of course, Team Rocket is an S-tier team. They are often the first team fans think about in Pokemon, and they have been in the most games compared to other teams as well. Their goals are simple to understand: thievery of Pokemon. The fact that their leader is a Gym Leader, while now known by all, was a well-done twist. Jessie and James, while more well known in the anime, are also fan favorite characters that sometimes appear in the games.
This team alone is S-tier, as other teams are hard to compare to Team Rocket. Team Rocket is nostalgic, classic, and unforgettable. The developers know this, and that is why they have appeared in many games. They have appeared in Pokemon Blue, Red, HeartGold, SoulSilver, and many more; they even return in Ultra Sun and Ultra Moon as Team Rainbow Rocket.
A Tier
Team Skull was a refreshing take on a villain team. They were introduced in Sun and Moon, and were adored by the fandom for their hilarious arm movements and wannabe gangster aesthetics. They were not exactly evil either, as they were a team of teenagers that seem to be lost souls finding community in delinquency. Their leader, Guzma, was particularly popular, as it is hinted he had big ambitions but fell from grace.
Team Plasma is A-tier because of two characters in the team: N and Ghetsis. N has become a fan favorite character out of all the Pokemon games due to his unique backstory and eccentric personality. Ghetsis is more than an evil team leader, but is hinted to be an abusive father to N. That is a whole level of evil that sets him apart from other team leaders.
Team Magma and Team Aqua are also A-tier. They have a level of nostalgia and are also quite fun in their rivalry. Most evil teams are alone in their Pokemon generation, but Magma and Aqua coexist in their region with opposite but evil goals, to either expand landmass or the sea. Maxie and Archie are not only fighting with the protagonist, but each other as well, which is a cool aspect of them that other teams do not have.
B Tier
Team Yell from Sword and Shield can be more easily forgotten, but had original ideas and interesting writing. They were a little similar to Team Skull in that they were delinquents rather than actually sinister. What was original about them was they were overly devoted to Marnie, and thus caused a lot of issues. It was very interesting to see, as Team Yell reflected some uncomfortable truths about fans that go too far.
C Tier
C-tier villain teams are those that made very little impact on the Pokemon fandom. They are often forgotten due to their lack of unique qualities and goals. Team Galactic is a C-tier, as their goal is pretty vague and the leader Cyrus lacks unique qualities. Their goal is to create a new universe that Cyrus could rule over, which isn't particularly unique. Pokemon Legends: Arceus freshened up villain team a little by showing their ancestors and unexpected backstory.
Team Flare is another C-tier team that had potential. They claimed to be motivated by just money and planned to make themselves as stylish and rich as possible. However, that was a ruse and the real plan was to destroy all life except for themselves. This plan is very evil, but ultimately more boring than the ruse.
Pokemon Scarlet and Violet will release on November 18, 2022 for the Nintendo Switch.