[Kamen Rider Lucha]

Ohhh, I love this question! Villains are generally my favorite part of Sentai. If a show has lackluster villains, it usually (though not always) fails to really engage me.

Here's my list, in chronological order...

Igam from Maskman, because of their fabulous gender fuckery.
Maria from Jetman, because her arc is beautiful and made me cry over and over again.
Radiquet from Jetman, because he is fully batshit insane.
Matoba Jin from Dairanger, because he's the cruelest motherfucker in existence.
Junior from Kakuranger, because he's Billy Idol that sometimes looks like a punk camo skeleton and shreds on guitar.
Rio and Mele from Gekiranger, because of their honor, depth, and dedication to one another.
Dayuu from Shinkenger, because of her profoundly tragic backstory.
Juuzo from Shinkenger, because of his unrelenting nihilism.
Enter from Go-Busters, because of his flamboyant cruelty.
Schwartz and Gritta from ToQger, because the prove that love can bloom in the darkest circumstances.