One show at a time. The below list includes my favorite complete television series, and my favorite episode or few episodes. For me, it's interesting to see which ones I have a clear favorite for.
It's fair to say that yes, there will be general spoilers. Be careful.
Star Trek: The Next Generation
Darmok, Season 5, Episode 102
In this episode, Captain Picard gets stranded on a planet alone and he has to learn to communicate with an alien captain - a Tamarian - who speaks in metaphors. As if that wasn't hard enough, a dangerous beast is trying to kill them. To save themselves, they have to understand each other.
It might have been my age when I first saw this, but this is one episode that always sticks with me. I remember being fascinated by the concept of a language based on that race's myths and histories. I haven't seen this episode in a long time; somehow my collection of TNG stops at season 4. I think it will hold up though.
All of them.
What an out, huh? But every time I rewatch the single season (sniffle), I usually say something along the lines of, "damn that's a good show" when the credits start to roll for every episode. If I had to pick one weak episode, for me it was The Message.
I'm going to go have a moment for all the lost potential now.
Whew, there are several. I was blown away by this show, and it only barely out ranks Firefly as my favorite TV show ever. Season 3 is my pick for the best overall season.
Exodus Part II, Season 3, Episode 36
Galactica burning through the atmosphere on New Caprica. Enough said.
Crossroads, Part II, Season 3, Episode 53
Almost all is revealed. We learn who four of the Cylons are. Lee Adama makes a kick-ass speech at Baltar's trial... I remember staring at the television for a minute after this episode ended, entirely surprised that they gave us that many of the Cylons at once. Well played Misters Eick and Moore, well played.
Buffy the Vampire Slayer
The Gift, Season 5, Episode 100
I might get thrashed for picking this one, but I found the whole Glory plotline intriguing and this episode to be a solid end to an epic fight. I mean, come on:
"Dawn, listen to me. Listen. I love you. I will always love you. But this is the work that I have to do. Tell Giles... tell Giles I figured it out. And, and I'm okay. And give my love to my friends. You have to take care of them now. You have to take care of each other. You have to be strong. Dawn, the hardest thing in this world... is to live in it. Be brave. Live. For me." - Buffy
Once More with Feeling, Season 6, Episode 107
A musical episode of Buffy? Hell yes. I listen to the soundtrack for this a lot. So many strong emotions and key parts are conveyed through this singing though. I always tear up during "Something to Sing About."
Threads, Season 8, Episode 818
I love SG-1, and I don't care who knows it. I find it to be fun, entertaining, full of great characters, and some truly wonderful moments. I think Threads showcases the best of the series.
I've watched this particular episode countless times. Part of it is the way the Ancients plotline is woven in and played out, part of it is definitely Mel Harris as Oma, part of it is the huge emotional scenes that play out - if you haven't seen it, I don't want to spoil you. A lot of big things happen in this one episode. It is emotionally jarring to watch. To me, that screams good TV.
Not Fade Away, Season 5, Episode 110 - series finale
I don't think I've ever seen a show end any better. Granted, there was the typical Joss Whedon cruelty and pain, but still. I usually come away from series finales with questions or confusion or nitpicks - but not this one.
Smile Time, Season 5, Episode 102
Muppet. vampire. If you don't find this episode to be hilarious, I don't know if we can be friends anymore.
What are your favorite episodes from these shows?