Great suggestion! Everyone remembers the Gorn, but the Metrons are fairly representative of the incredibly advanced aliens typical of TOS (like the Organians, Thasians, or Providers).
I think I’d suggest a planet-of-the-week episode. From TOS, “This Side of Paradise” or “A Taste of Armageddon.” From TNG, maybe “Who Watches the Watchers” or “Up the Long Ladder.”
I love this! Now you need to do an analysis like this one on Star Trek and the Bechdel-Wallace test!
I realize you’re not trying to predict quality, just personal enjoyability, but I do wonder how it relates to quality.
I actually think it might be slightly more predictive of the quality of a show overall than of individual episodes. But both ST:TOS and ST:TNG have many great captain-centric episodes that I’m not sure if it is predictive of episode quality particularly.