Name Your Favorite Episodes and Why

1. “The City on the Edge of Forever” (#28): Powerful, reverent and tear-inducing—television of the highest order. A plot so good they recycled it in “All Our Yesterdays” (#78) and Star Trek IV.
2. “The Naked Time” (#7): It’s got everything a viewer might be in the mood for—mystery, drama, comedy, romance, action and suspense. It also happens to be one of the best episodes to get to know the characters, seeing as how they all ‘let loose.’
3. “Where No Man Has Gone Before” (#2): It’s a one-of-a-kind debut testifying that Star Trek was a winner right out of the gate. The momentum of interest, mystery and suspense mounts, culminating in the kinetic climax.
4. “Space Seed” (#24): Khan is a well-defined, charismatic characters. Yeah, he’s egomaniacal and chauvinistic—certainly no one you’d want to have as a friend or emulate—but no less an outstanding character.
5. “The Galileo Seven” (#14): Spock’s struggle to logically command a small group of illogical humans is captivating.
6. “Arena” (#19): Unforgettable, gripping and eminently entertaining.
7. “Shore Leave” (#17): It’s great fun seeing the crew take a frolic through the park, and what a wild park it is!
8. “The Doomsday Machine” (#35): It has edge-of-the-seat suspense throughout and the grotesque doomsday machine is Jaws on a galactic scale.
9. “This Side of Paradise” (#25): It's amusing to see the stoical Vulcan happy & in love for the first time in his life, expressing emotions he’s kept pent up all his days.
10. “Journey to Babel” (#44): An exquisite combo of Spock's parents, a ship full of extraterrestrials, action, intrigue and heartwarming climax.
11. “Mirror, Mirror” (#39): Seeing the yin of the Federation yang is both fascinating and absorbing.
12. “The Devil in the Dark” (#26): Exemplifies Trek’s credo of exploring “strange new worlds to seek out new life,” its philosophy of respect-for-all-life-forms and the conviction of finding solutions that don’t involve needlessly killing an entity

My all time favorite is The Tholian Web from season 3. The plot is compelling and suspenseful; even a bit Lovecraftian.

Runners up include Mirror Mirror, Balance of Terror, and Galileo Seven.

I always love episodes in which Spock conducts investigations or when Scotty is acting captain.

The Menagerie, to see Jeffrey Hunter as the original Captain and Susan Oliver all green.

Well, let's see. As far as high adventure goes I choose Balance of Terror and The Doomsday Machine. The Trouble With Tribbles and I Mudd were the funniest, and The Cloud Minders and Let That Be Your Last Battlefield receive kudos for social significance (The Cloud Minders society was similar to the then-existing apartheid South African government, Let That Be Your Last Battlefield showed the tragic result of everybody not being able to get along).

"The Doomsday Machine" - Need I even say why.

"Balance of Terror" - Because it sacrilege if this isn't one of your favs

"The Changeling" - Nomad is just a funny little dude who you can't afford to piss off

"Space Seed" - Ricardo was just pimp cool. He was a great actor.

"Mirror, Mirror" - Just because Spock was cool af with the beard.

"Let This Be Your Last Battlefield" - Lou Antonio and Frank Gorshin were beyond incredible. IMO, this was the best-written episode of the series.

For comedy, The Trouble With Tribbles.

For high adventure, The Doomsday Machine.

For social significance, Let That Be Your Last Battlefield.

For interpersonal drama, there are so many to choose from I won't even try.

My favorites were:

A Taste of Armageddon.

I just enjoyed how Kirk went all out to get rid of their "neat" war so they'd have to make a choice.
I liked seeing Scotty run the Enterprise and stand up to the mousy diplomat trying to get them to lower the screens.
Being ready to use General Order 24. I enjoyed the entire thinking, chess match strategy going on.

Balance of Terror

I liked the tactics and chess maneuvering each captain was having to use to out think the other on a space level, using powerful advanced war ships.

Without ranking them

Season 1
Balance of Terror : Solid episode introduces Romulans and Mark Lenard performance as the Romulan commander was very good.
The Menagerie (The Cage) : The idea of aliens playing with your mind is very powerful sci-fi for the time. Spock's loyalty shines in this episode, the Court Martial scenes were terrible thou.
Space Seed : Introduces Khan and his geneticly engineered perfect humans, Ricardo Montalbán steals the show with his Khan performance.
A Taste of Armageddon : It's the first Star Trek story I stumbled upon originally as a photonovel comic from the late 70's so for me it's a special episode.
Errand of Mercy : First appearance of the Klingons in Trek lore.
City on the Edge of Forever : Best episode of TOS, everything was perfect for a production of that time.

Season 2
Amok Time : Spock being angry and throwing food is priceless
The Doomsday Machine : Very solid story and Commodore Decker was the star of the show very good performance from the actor.
Mirror Mirror : Evil not so evil Spock with goatee !
Journey to Babel : Spock and his conflict with Sarek, introduction to Sarek and Amanda. Well executed episode.
The Trouble with Tribbles : It's a very entertaining light funny episode.
Patterns of Force : Star Trek meets Nazi's
Assignment Earth : I know it's somewhat one of the silly episodes but it has Teri Garr and time-travel.

Season 3
The Enterprise Incident : Romulans are back and another very well written episode, a highlight in the terrible 3rd season.
All Our Yesterdays : It's only good for me because I liked the McCoy and Spock interactions, Spock's love interest was also a highlight of the episode.
Day of the Dove : I only like this episode because it has Klingons.

Don't have much love for Season 3 everything was going downhill.