As a kid, I always thought team Galactic, Plasma and Skull were the best evil teams due to their stories, but now that I'm older I have formed a new-found appreciation for Team Rocket, especially after replaying Gens 1/2 and really paying attention to the dialogue and little bits of worldbuilding.

Like, they really knocked it out of the park with their first attempt. A gang who steals and sells Pokémon to make money. I mean, it just does not get better than that when you think about it. It's simple, but it's great BECAUSE it's simple. The concept of Team Rocket just works so well in the world that is established in the first two Gens and the style of storytelling in those games.

It's the best because it's the most grounded, which is funny considering Giovanni's team. Team Skull was the closest we ever got to an evil team as good as Team Rocket, but Team Rocket still takes the crown, easily, mainly because Team Rocket doesn't rely on legendaries like the newer Gens do, and how well they are portrayed in the early Gens.