Sir Patrick Stewart is probably one of the most respected Shakesperean actors of the last 30 years. Star Trek: The Next Generation is arguably what made him so famous.
But there's another TNG actor who was already enormously famous in 1987 and repeatedly challenged Stewart to up his performance in every episode see appeared: Whoopi Goldberg.
Whoopi was so famous at the time that Star Trek: The Next Generation started, its executive producers didn't think she was serious when she said she wanted to be on the show. But Whoopi was a huge Nichelle Nichols fan (as are we all) and she just wanted to carry on the socially-responsible torch that Nichols had in the '60s.
Guinan was the result and, despite her infrequent appearences, she's easily one of the best characters in the history of Star Trek. Even though she was only in a handful of episodes, it was nearly impossible to choose only five quintessential moments. But I did it (as I did for Beverly Crusher, as well). You are welcome.
Guinan explains slavery to white people
If there's one thing Star Trek: The Next Generation is known for, it's endless moralizing. I like it, personally. Morality plays done well are great and TNG had a solid track record with them. In fact, one of the first truly great episodes TNG had was an episode called "Measure of a Man," in which there is a hearing to decide whether or not Data has the right to decide his own fate. Is Data sentient? Is Data just a machine that is the property of the Federation and, blah, blah, blah we get it: this is about slavery. Set TNG moralizing to MAXIMUM SETTING.
But, wait, friend: you can't just have a great white hope roll in and solve slavery, because that's weird. Equally (if not more) weird would be to bring in Geordi to explain slavery, on account of LeVar Burton already played Kunta Kinte in Roots and, yeah... that would be a just a touch on the nose, don't you think?
Enter Guinan to calmly explain racism to Picard. The best moment from this conversation is when Picard figures out what Guinan is saying and calls slavery, you know, slavery. Then Guinan says "I think that's a little harsh" specifically to test Picard's wokeness. He passes, but he still had to have slavery spelled out for him so, uh... point to Guinan for being the only one to actually respect history in the 24th century, I guess.
Guinan forks Q
These are two moments, but they are effectively the same greatness so I'm considering it a tie. Guinan is, to our knowledge, at least 600 years old. She may be way older, though. And she did a lot in those centuries. She hung out on Earth in the 19th century, she had a Tarcassian razor beast as a pet, and she used to be besties... with Q. Talk about shows I wish I could see: evil Doctor Who but starring John de Lancie and Whoopi Goldberg? Damn, son! Sign me up!
Alas, we only see the Q/Guinan aftermath. We do know Q is super abusive based on how he treats Vash in the DS9 episode, "Q-Less," though, so I think it's safe to say that Guinan is 100% in the right when she whips out those weird mantis-like fighting moves in "Q Who" and is 200% correct to stab Q with a fork in "Deja Q" to test that he's actually lost his powers.
Which is the better moment? I dunno, dudes. In the former we find out Q and Guinan were buds, which is amazing, but the latter involves Q getting forked by Guinan. I can't choose. I leave this Guinan's Choice to you.
Guinan makes Riker captain up
There are TNG speeches and then there is the cold shower pep talk that Guinan gives Riker at the beginning of "The Best of Both Worlds II," in which she demands that Riker completely let go of Picard now that he has been Borg'd. "You can do it" is nice, "I did it and you better do it too or we're all dead, my dude" is better. And that's basically the speech Guinan gives to Riker. It's also the first time she talks about how she and Picard's relationship goes deeper than friendship or family, which... yeah, we'll talk about that later.
In short: there is an alternate timeline from "Parallels" where Riker is still running from the Borg and that is clearly the timeline where he ain't got that Guinan speech.
Guinan says LOL nah to Borg sympathizing
There are two moments from "I, Borg" that both qualify as best Guinan moments, but I am choosing the conversation with Guinan and Geordi over the one with Guinan and Hugh, the Borg, for reasons I think will become obvious.
So, all right. We are all aware that Guinan's people were nearly wiped out by the Borg, yes? Just a bunch of pasty colonizers rolling up, destroying her world and assimilating her people into robotic, slave drones. It's, uh... not a subtle metaphor. And it isn't made any more subtle by the fact that this conversation over the fate of a young assimilating Borg, Hugh, is between two people of color.
It is understandable, I feel, that Guinan is not interested in humanizing Hugh. As she says, when Hugh's "big brothers" come for him, "they won't stop until they destroy us." Why have doubts when you know the opposition's sole goal is to end you and your culture?
But Geordi, whose job it is to turn Hugh into a walking bomb, has spent time with Hugh, and now the waters are muddy for him. Geordi is getting through to Hugh. And if he can pull one young Borg and deprogram him, isn't there a chance for the others?
It's not so cut and dry, in Geordi's view. Ultimately, Guinan does speak with Hugh and sees shades of humanity in him. But, I think Guinan's first assessment of the Borg and Hugh is more honest and true to life. And true to the world we're living in right now, if you want to get really real today. Just because you calmly explain that white supremacy is bad to one young Nazi doesn't make Nazis go away.
Guinan and Picard - the truest love of all
And now it's time for a little wish fulfillment. You know how SYFY is doing that whole #ItsAFanThing 25th Anniversary Celebration? Well, one of my favorite fan things is to see a hypothetical opening for something sexy and make it my personal canon.
For that reason, my favorite Guinan moment is from "Time's Arrow Part 2" when she and Picard are trapped in a cave together. Now, keep in mind, for Guinan, this is the first time she and Picard meet. And that moment, while not the best, is very hot. Like, Picard gives Guinan some crazy bedroom eyes and that was when I was like, "Oh, snap, that's what Guinan meant about being closer than friends and family and whatnot." They've been a secret couple this WHOLE. TIME.
And if you want to go ahead and be a fool and doubt my claim, there is the best Guinan moment of all in this cave when Picard is straight up romantically cradling this woman. You know the whole Doctor/River Song schtick where they meet in the wrong order? Well, Guinan and Picard did it first, friends.
You can say what you will, you can point out that we never see them kiss, but their love is real. Just like Stewart and Goldberg brought out the best performances in each other, I believe that Picard and Guinan are the only romantic pairing right for each other.
Also, I'm pretty sure the reason Guinan won't help Riker figure out how to get Picard back to the 24th is because she's secretly hoping time will be rewritten and Picard will stay in the 19th with her. Guinan, please know: I get you. I wish it could've worked out because you and Picard make the best, uh... moments of all.