While it's hard to think of a substandard episode from season one, whenever I want to recommend this series to anybody, this is the one I suggest they sample to see how wonderful a TV show can be. From the beginning to the twist ending, through the wonderful (uncredited) NASA play-by-play by Don Fedderson veteran Paul Frees (six seasons of THE MILLIONAIRE as The Millionaire John Beresford Tipton), the perfect familiar versimilitude of the family of brothers, father, grandfather and dog, I can't imagine anything more pleasurable to experience. (My other favorite from this first season is the suspenseful season-ending "Fire Watch." And even now, I'm rembering others which stand out, making me a liar to pinpoint just one as my only "favorite.")
All of this quality is made more starkly obvious having waded through the last several seasons of the series in syndication to get to the point where the episodes begin over at season one, despite the show remaining under the series' best writer, George Tibbles' control through the end. (Of course, by then, he'd lost Mike, Robbie, Sally, Sudsy, Hank, the show's heart, Bub by attrition, and except for several small token appearances, Chip, as chess pieces, leaving him and Fred MacMurray with three wives, a stepson, a stepdaughter, an unlikable uncle, and three non-speaking triplets as the series nominal eponymous characters, so you really can't blame him that by season 12, the show had totally run out of gas.)
So, as a rule of thumb, if the episode is in black and white, you're watching one of the good ones. And this one is the best.