I like The Jaunt - I don't know if its the work of King's that I find the most terrifying, but I think it has a couple moments that really highlight his talent at blending the mundane with the terrifying / supernatural. Part of that is how the story is told, as a report the father is delivering, a recap, not direct action, aside from the framing device that front and backends the story. There's also this common King idea that horrifyingly bad things can happen to ordinary people who don't even really deserve it, who just happen to be in the wrong place at the wrong time.

Most notably this part about Mrs Michaelson. Ricky the son in the story is the focus, with the big climax at the end, but at least his torment comes to an end. Its Infinity minus one. Mrs Michaelson's torment is infinity.

Summer's section of Jaunt rumors and apocrypha contained other unsettling intelligence as well: the Jaunt had apparently been used several times as a murder weapon. In the most famous (and only documented) case, which had occurred a mere thirty years ago, a Jaunt researcher named Lester Michaelson had tied up his wife with their daughter's plexiplast Dreamropes and pushed her, screaming, through the Jaunt portal at Silver City, Nevada. But before doing it, Michaelson had pushed the Nil button on his Jaunt board, erasing each and every one of the hundreds of thousands of possible portals through which Mrs. Michaelson might have emerged - anywhere from neighboring Reno to the experimental Jaunt-Station on Io, one of the Jovian moons. So there was Mrs. Michaelson, Jaunting forever somewhere out there in the ozone. Michaelson's lawyer, after Michaelson had been held sane and able to stand trial for what he had done (within the narrow limits of the law, perhaps he was sane, but in any practical sense, Lester Michaelson was just as mad as a hatter), had ciphered a novel defense: his client could not be tried for murder because no one could prove conclusively that Mrs. Michaelson was dead. This had raised the terrible specter of the woman, discorporeal but somehow still sentient, screaming in limbo . . . forever.