Cher Lloyd, Indigo2, London; Sufjan Stevens, Barbican, London

Every year, despite my better judgement, I find myself getting sucked into The X Factor, and every year there's one contestant I'm rooting for. She may have finished fourth, but the 2010 series belonged to Cher Lloyd, the tatter-kneed teenager who utterly owned the audition stage with her staggering rendition of Keri Hilson's "Turn My Swag On", a then-obscure R&B track. But by the time she'd spent 12 weeks as a performing seal for Cowell and co, she was every bit as broken and compliant as Winston Smith after his stay in Room 101.

If any of Lloyd's auditionee arrogance was left, she'd never have agreed to her first single, "Swagger Jagger", being essentially a Haribo-pop remake of "Oh My Darling Clementine". Her debut album Sticks + Stones was equally flimsy, and, apart from the insanely catchy faux-Latin pop of "Superhero" and the satisfying anger-grunts of "Want U Back", its shortcomings are highlighted in her live show.

Strutting about in a black lace shrug and vertiginous heels, she pads out her own material with covers of Jason Derulo's "Breathing", Avril Lavigne's "Complicated" and Usher's "OMG", as well as "Playa Boi", which is Neneh Cherry's "Buffalo Stance" in all but name. The good taste displayed by choosing Robyn's peerless "Dancing on My Own" is negated by slowing it down to a dreary ballad. "I do wish I would have wrote it," she says, and somewhere a grammarian weeps.

Even the eight-year-olds look bored. There's a feeling that this isn't working out. Despite a No 1 single and a top-five album, Cher is playing the Indigo2 while fellow X Factor also-ran Olly Murs can fill the 02 next door.

It's as though she's already preparing to disappear from view. Reading tweets sent by fans, she answers a question about which superpower she'd most like to have with "I think I'd pick the obvious one: to be invisible". Give it a year, luv.

Three things I know about Sufjan Stevens: he's the butt of many a Shaky joke; he once attempted to record a series of albums about each American state but gave up after two; and he's something of a sacred cow to the sort of people who read Pitchfork Media. None of which matters tonight, because the Detroit singer's latest London show is a new collaborative venture with film composer Nico Muhly and The National guitarist Bryce Dessner which requires no prior knowledge.

The main event is a concept piece about the Solar System, with the Navarra String Quartet , Muhly, Dessner and Stevens joined by the New Trombone Collective for 10 pieces in a psych-classical style, all vocoders, twinkling keys and orchestral crescendos. It's vaguely reminiscent of Pink Floyd circa Dark Side of the Moon meets The Flaming Lips circa The Soft Bulletin.

A saggy orb hangs overhead, its colour shifting with each movement. The approach is either astronomically literal or mythical: Neptune takes the king-of-the-waves angle and Jupiter is full of "by Jove" puns. Mars gets a discordant piece about a castrated warrior, Earth an auto-tuned elegy about the loss of innocence. There are titters when Stevens points out that the comedy staple Uranus is made of, among other things, "frozen methane".

Visually, it's like a school trip to a slightly rubbish planetarium; musically, Stevens is no Gustav Holst. After apologising for how "dark and nasty" it has all been, he admits it's "still kind of a work in progress", inviting the cynic's response to any piece of experimental music: come back to me when it's finished.