Jashinka in Dynaman- Aside from being racists, they were also believers of the survival of the fittest even among themselves.
Gozma in Changeman- Bazoo spared the strong and destroyed the weak. In fact, Ahames carried out the idea of survival of the fittest to greater heights. Bazoo further emphasizes this because most of them don't serve Bazoo at their own free will, it's only because he's the strongest.
Mess in Flashman- They treated every specimen as experiments to seek to create the strongest organism.
Tube in Maskman- Ever since Zeba took over the throne by force, the once peaceful kingdom became a place where strength rules all. Sice Zeba is the strongest (being in reality Lethal Dobler II) so he rules above everyone else.
Volt in Liveman- They regarded that only they are fit to rule above humanity. They had the survival of the fittest in the sense of the intelligent rule over the stupid.
Zone in Fiveman- They were similar to Gozma in its patterns. They preserve the strong and destroy the weak.
Vyram in Jetman- Radiguet, Maria and Tran all gambled to whoever beats the Jetmen will rule over them. Radiguet was for me a bloody, genocidal maniac of questionable sanity who believes everybody is just below him and will do anything to rise above anyone who is stronger than he is, redefining the cruelty of survival of the fittest.
Gorma in Dairanger- The succession of Gorma Emperor's wasn't a good one. In fact, most of them involved the previous emperor being slain by the succeeding emperor. Power rules over the Gorma which causes several civil wars inside it.
Evorian in Abaranger- Aside from being racist, I believe they also rule by survival of the fittest. The name seems to be a pun evolution.
The Gen Juken in Gekiranger- Long believed in survival of the fittest and demonstrated it from subtle to sheer pure evil when he murders people just for the heck of it to get rid of his "boredom". In fact he mistreats and manipulates his subordinates because they were not "strong enough".
Jaryuu and the Questers in Boukenger- These two groups in Boukenger are the most cruel. Okay Yaiba is sick but not as sick as Ryuon (who Mr. Smith counts as a "softer" Radiguet) and the Questers consider themselves better than humans because they have super powers. I'd like to also say that the Jaryuu select the strongest by letting them literally kill each other to death.
Missed any? Let me know!