I'd like to write about attitudes taken toward the prime directive in Star Trek, potentially including all of the TV series within the original timeline (esp. OS, TNG, VOY, DSP), and need some touchstone episodes on which to base my conclusions. Recognizing that the prime directive is an overriding theme that can be related to almost any episode in any series (it is, after all, "prime" ...) I'll narrow that down:
What shortlist of Star Trek episodes deal most explicitly and continuously and with a moral conflict that arises directly in reaction to a consequence of the Prime Directive, in the context of a technologically advanced people (i.e. Starfleet) encountering a primitive or powerless people, and feeling compelled to intervene, whether due to moral or political interests? And with the crux of the episode turning on whether the prime directive is followed or ignored?
More informally, high quality writing, big stakes, interesting real world political analogues, and iconicism within Star Trek fandom lore are all other good criteria.