One single hour of television that brings a smile to your face every time you remember it? For me, it’s a special Harry Anderson did called “Hello, Sucker!” which aired on Showtime back in 1985, I believe. He talked about con games, showed a compilation of tricks from the magic tour he did back then, and threw in a few very funner fillers. I will never be tired of watching that show.
Off the top of my head it’s hard to recall, but probably something from either Blackadder or Father Ted. They’re both shows I can’t watch late at night because I’ll wake up everyone else by laughing too loudly.
I can’t say it brings a *smile *to my face, but “Ozymandias” from Breaking Bad is the best I can remember having seen recently.
A couple of Sherlock’s have seemed more like an event than just a show, and lived up to expectaion. An advert-free ninety minutes though.
“The Germans” from Fawlty Towers.
I bought the boxed set for my father and we watched The Germans together and nearly passed out laughing.
Rick Reynolds, Only The Truth Is Funny special.
Hard to pick just one.
The LOST episode The Constant would have to be up there.
Firefly’s Objects in Space is a contender as well.
I’d have to do some cut and paste: Never Mind the Buzzcocks, Season 18, episode 3 hosted by Ricky Wilson (wherein Ryan Jarman claims to have invented Live Aid), and NMTB Season 20, episode 2 with Donny Tourette and Noel Gallagher as guests, when Tourette is a cheerfully dim-witted insufferable twat for 30 minutes.
Runner-up: Same show, the SE19E05 with John Barrowman as a guest when he “out-gays” host Simon Amstell (“Talk to the hand because my wrist is pissed!”) and S18E05 with Jeremy Clarkson guest-hosting with Trisha Goddard (“Is it going to be sexist jokes all night?”), Jim Jeffries (“Over here, yeah - do what you like on that side!”), Rick Wakeman of Yes (“Yes was awarded most shit band ever.”) and Antony Costas of Blue (“Bad news for Rick, but Blue breathed a huge sigh of relief.”)
I’d have to say it’d be Bonanza - Hoss and the Leprechauns - we look forward to it ever year around St. Patrick’s Day.
ETA - Tangent - I totally agree - it IS hard to pick just one. The more I think about it the more I can come up with. 
I have trouble picking a clear favorite from the many candidates, but the series finale of Six Feet Under came immediately to mind. There are plenty of other complete series that I liked more overall, but when it comes to narrowing it down to just one hour, that episode’s hour was pretty damn powerful.
The Carol Burnett Show. Repeatedly.
I wouldn’t say it brings a smile to my face, but probably the best hour of TV I’ve seen is the *House *episode “Three Stories.”
For smiles, I’m gonna go with either the *Father Ted *episode about the fun fair, or the last 60 minutes of “Day of the Doctor” (the 50th Anniversary *Doctor Who *special).
The “Three Stories” episode of House is one I have cited previously in threads on this topic.
ETA: Aaaand… Beaten by 11 minutes!
Another “not a smile” answer, but it’s a three way tie between “Objects in Space” (Firefly), “The Body” (Buffy the Vampire Slayer) and Season 2, Episode 5 of Call the Midwife (I don’t think they have names, but if I call it “The Abortion One,” fans will know which one I mean.)
Punches in the gut, all three.
Oh! And how could I forget the *Doctor Who *episode “Blink”?
That’s good one. Carol, Tim, and Harvey may have been the best 1-2-3 comedy combo there ever was.
The moon landing, regardless of its duration. And yes, it was real.
For me that would just have to be the hour around:-
July 20, 1969, at 20:18 UTC
thats not one I am ever going to forget.
Nor is the hour around:-
The South Tower collapsed at 9:59 a.m.
not the best, but one that stays with you all your days.
Ha … simulpost 
BtVS season 5 finale, The Gift. Dunno if it’s the best hour of TV, but it’s my favorite.
Ben: She could’ve killed me.
Giles: No, she couldn’t. Never. And, sooner or later, Glory will reemerge and make Buffy pay for that mercy. And the world with her. Buffy even knows that, and still she couldn’t take a human life. She’s a hero, you see. She’s not like us.
Ben: Us?