Top 3 episodes (all series) for a newbie

Both me and my gf started with entire lower decks, then snw and now ive started tng (from start, currently in s2 snd enjoying more than i thought based on all the recs to go straight to s3).. That has been a great entry for us at lesst

TNG and DS9 are the only two series that I really know well enough to make these recommendations for.

I would highly recommend watching TNG before DS9, even if she likes DS9 better. TNG and DS9 work best as companion shows, with TNG building up a lot of DS9 plot-lines in its latter seasons. I would also highly recommend against starting with any episodes involving Q or the Borg, or any of the series "highlights". Let those plots build, and you don't want to spoil some of the best episodes in a sampler. My go-to TNG introduction picks are:

-Cause and Effect

-Darmok

-Measure of a Man

DS9 can be harder to pick introductory episodes for. Its more serialized nature means that a lot of later episodes have a lot of spoilers. I would highly recommend against picking any episodes that highly involve the Dominion or the Dominion War, let that plot build itself up. That does however, leave us with a lot fewer options. My DS9 introduction picks are:

-Duet

-Past Tense

-Bar Association

In no particular order, two-parters count as one episode.

TOS:

• Balance of Terror
• The Trouble with Tribbles
• The Doomsday Machine

TAS:

• The Infinite Vulcan
• The Slaver Weapon
• The Lorelai Signal

TNG:

• Measure of a Man
• The Inner Light
• Cause & Effect

DS9:

• Pale Moonlight
• Past Tense
• Far Beyond the Stars

VGR:

• The Killing Game
• Latent Image
• Scorpion

ENT:

• Regeneration
• A Night in Sickbay
• A Mirror Darkly

Those are the only series I’ve seen in their entirety, so I’ll leave it at that.

"Data's Day" is actually a pretty great one to get someone into TNG, it's fun, but most importantly, Data is essentially walking around introducing all of the main characters to the audience.

I typically recommend starting with TNG in general (I used to say because it was "modern" 😭) as it naturally leads into DS9 and VOY. That said if your friend doesn't typically watch older shows but is open to them, then just starting with SNW or ENT is an excellent intro to the rest of Trek.

TOS: Balance of Terror, The Doomsday Machine, City on the Edge of Forever

TNG: The Measure of a Man, Yesterday's Enterprise, Deja Q

DS9: Progress, Duet, Trials and Tribbleations

VOY: Body and Soul, Year of Hell, Tuvix

Specifically for a new viewer who wants 3 shows that would be different and enjoyable:

TNG:

The Inner Light, Cause and Effect, Lower Decks

DS9:

Duet, The Visitor, Trials and Tribbleations

TNG: Drumhead, I, Borg, and Chain of command (or if you don't want a two parter, take your pick of Q who, Measure of a Man, or Yesterday's Enterprise)

DS9: In the Pale Moonlight, Inquisition, and It's Only a Paper Moon.

VOY: Living Witness, Tuvix, and Year of Hell (or again, if you don't want a two parter, go for Tinker Tenor Doctor Spy)

TOS: The Devil in the Dark, The City on the Edge of Forever, and Mirror Mirror.

ENT: Similitude, Regeneration, and In a Mirror Darkly (don't really have a good non-two parter to suggest over In a Mirror, Enterprise doesn't have a lot of great standalone episodes IMO)

Movies: if you want to use these as examples, The Wrath of Khan for TOS and First Contact for TNG.

And I don't really have a list for LD, PIC, DIS, SNW, or PRO.

Edit: for VOY, I might actually put Author, Author over Tinker, Tenor, Doctor, Spy.