IMO, the first episode of Liveman is just about the coolest first episode I've ever seen in a tokusatsu. I love the setup, it's one of the first sentai premieres to take its time and not rush into everything. I love when Yuusuke and the gang first lay eyes on Tsukikage and the gang after they wiped out Academia Island. And then our heroes reveal they have powers, too! The look on the villains' faces is priceless. Have we ever seen villains actually scared that someone is opposing them? It's usually always a speech of fake confidence. And then our heroes go and get their asses kicked, a rarity in a first episode.
While Agito's first episode might not have the punch of the rest of the series, I'll always like it for Agito's first appearance -- being revealed in the dark by the fire of an explosion. And then "Believe Yourself" kicks in.