Bo Burnham, Pleasance DomeDaniel Sloss, Pleasance DomeJosie Long, The CavesJennifer Coolidge, Assembly RoomsThe Boy with Tape on His Face, Gilded Balloon

It's often said that stand-up comedy is a young man's game, but a teenager's one? Disconcertingly, two of 2010's hot tickets prove that being born in the Nineties is no barrier to bringing the house down.

Bo Burnham is a 19-year-old US songwriter-comic to whom the word "sensation" clings: having garnered 60 million YouTube hits, he's now receiving breathless acclaim for his Edinburgh debut. A whirl of piano-pop, poetry and stand-up, it casts him as a trenchant malcontent trapped inside a fey indie kid's body, the tone set by his declaration: "My ex-girlfriend had a weird fetish. She used to dress up as herself and act like a bitch." No topic is too lofty for his desecration, be it the habit of art or the comfort of religion, and the one-liners come thick and fast. He's a commanding keyboardist, laser-eyed stage presence and master of timing: a more consummate performer at this year's Fringe I've yet to see. If there's a gripe, it's that there's an underlying glibness to his verbal invention: what is this other than a display of his own cleverness? But that cleverness is dazzling enough for now. "I hate that term 'young comedian'. I prefer 'prodigy'," he says. Who are we to argue, frankly?

Fellow 19-year-old Daniel Sloss is hardly a prodigy, but he's an amusingly naughty boy nonetheless. The Scot begins with a wry expression of ageing angst at no longer being able to fit his hand inside a Pringles can. After that, however, it's schoolyard humour all the way, with riffs on mums, masturbation and music festivals. Envelopes remain unpushed, but he's good with terse quips ("I have two younger brothers: one's six years old, and the other's a dickhead") and makes a comic virtue of his greenness: he can't tell sex stories because they would "go along the lines of 'I had sex? Yes!'". His greatest weakness is audience banter; when he chides someone for their "fucking dull" job, it's clear he's yet to distinguish between edginess and obnoxiousness.

Now 28, Josie Long is coming into her own. Her decision to skip last year's festival allowed time for some epiphanies and these form the basis of Be Honourable, from her conversion to breakfasting to her realisation that "being nice" is no substitute for "doing good". Long remains endearingly whimsical, as shown by her obsession with breakfast photo- diarist Walter Ezell. But her love of incidental observation now comes aligned to an impassioned interest in the bigger picture: in a climactic call to political engagement, she laments her contemporaries' apathy and berates her former self as a "feckless child". Were a primer needed on balancing comedy's competing impulses, this is it: a show that slaps you around the face even as it offers you a hug and renders you hoarse with laughter. Meanwhile, she surely wins the best intro award for her impression of a formidable nail technician turned astronaut who "goes up space".

Representing Hollywood is Jennifer Coolidge, the blonde bombshell best known for her appearance as Stifler's Mom in American Pie. As she strides on in her va-va-voom LBD, you appreciate the injection of glamour into this most bedraggled of professions; sadly, she also stands out in less felicitous ways. Stumbling over her stilted script, she's a Jessica Rabbit caught in the headlights, her LA-centric insights – Paris Hilton? Vacuous! Tom Cruise? Weird! – over-familiar to a Martian. There's evident goodwill towards her, but this is little more than a glorified celebrity meet-and-greet.

In a city that never shuts up, for 30 days at least, silence is golden. Most welcome is The Boy with Tape on his Face, the miming alter ego of New Zealand's Sam Wills, and his buffet of visual skits – shoe puppets, one-man slow dances et al. When Wills involves the audience the show truly finds its muted voice: victims are forced to play along or "look like a cock", as the introductory voiceover warns, whether that involves humping along to Michael Jackson or recreating Ghost's pottery scene. Only the appearance of Alistair McGowan on Tuesday was out of synch with the show's homespun spirit. Some things are best left to the non-professionals.

Bo Burnham to 29 Aug, Daniel Sloss to 30 Aug (0131-556 6550); Josie Long (0131-556 5375) to 29 Aug; Jennifer Coolidge (0131-623 3030) to 29 Aug; The Boy with Tape on his Face (0131-622 6552) to 29 Aug