Gorangers- They were military-trained rangers based on capabilities by the military.
JAKQ- Four were selected to combat Crime based on their capabilities.
Battle Fever J- They were chosen based on their combat abilities.
Denziman- Not sure if they should be here.
Sun Vulcan- They were chosen by the Guardians of World Peace.
Goggle V- They were selected by the Future Science Laboratory.
Dynaman- They were handpicked by the Yumeno Invention Center.
Changemen- They were picked by the military and trained to see who will stand out. However I leave this area to some debate.
Maskmen- They were chosen by Sanjoru Sugata based on their martial arts skills.
Zyurangers- They were chosen from each tribe to be in the modern day based on their capabilities except for Burai who started out evil.
Ohrangers- Chief Counselor Miura chose the five best soldiers to be the Ohrangers.
Carrangers- Dappu selected them according to their race driving abilities despite most of them being kinda goofy.
Megarangers- They got chosen over some computer game. To be honest, that's kinda funny for a serious serious.
Timerangers The four rangers from the future were chosen based on capabilities. As for Tatsuya Asami, perhaps he was due to his karate skills but he was the only one from the present.
Dekarangers- They were chosen based on their performance as police officers in Special Police Dekaranger. Not everybody who works at SPD gets to be chosen. Sigh... did they really consider Banban Akaza's overenthusiastic attitude before choosing him?
Boukengers- Search Guard Successor chose them based on their capabilities.
Gekirangers- Master Sha Fu chose them based on their abilities in martial arts.
Go-ongers- The Go-on Engines chose them.
Goseigers- They were probably chosen for their abilities.
Gokaigers- Aka Red chose Captain Marvelous, Captain Marvelous chose the others. As for Gai Ikari, freaky how three dead rangers (Burai, Naoto Takizawa and Mikoto Nakadai) pay him a visit. Is Gai Ikari dead too?