One thing they tell us for sure is that the 19th-century classics have lost none of their appeal. ENB is currently hoping to net over 50,000 viewers for its spectacle-driven version of Sleeping Beauty in the Royal Albert Hall; the Kirov at Covent Garden is presenting the same ballet alongside other familiar classics. The strategy behind ENB's mass-scale Beauty is unabashed populism: the company has beefed up the ballet's glitz and sex appeal and is counting on the familiar Tchaikovsky score to lure the punters. Meanwhile the Kirov, which has lost much of its generous state subsidy, is fighting to build a mass audience with a staging driven by scholarship. Its four-hour Sleeping Beauty reconstructs the original 1890 production, complete with elaborate mime, processionals and historic costumes. The production sounds like only a balletomane's idea of fun, but the rapturous response with which it has been greeted suggests the public likes the real thing as much as the lite version.

But companies also need new works on which to stake their futures - even though the cost of making them has spiralled scarily and the box office gamble has become more intense. The Royal Ballet is thus lucky to have the new, small scale facilities of the Opera House's Linbury Theatre, where it can stage programmes of new works. This quasi-laboratory situation is a rare luxury, allowing choreographers to play outside of the pressured environment of the Opera House, and hopefully attract a more adventurous public than the traditionally conservative ballet crowd. The classics of the future may well come from here.

Zurich Ballet, under the rejuvenating direction of Heinz Spoerli, already performs a largely contemporary repertory - but it does so in part by maintaining a canny element of name recognition. The title of its London debut production Mozartina says it all: if there's any composer other than Tchaikovsky to snare the public, it's Mozart.

Spoerli's ballet is a kind of encounter between Mozart, his music and the 20th century. There isn't a narrative as such, although at its heart is a Mozartian figure (Michael Revie), who moves through the dancers with a quizzical detachment and an assortment of gimmicks, and may be supposed to offer an oblique comment on history. The dancers regularly change from 18th to 20th-century costumes and at one point Revie looks appropriately startled as huge rubber balls bounce around the stage with images of Mozart's face stamped on them. Frequently, a moving walkway delivers the dancers on and off the stage. Grinning and posing, they look like prizes displayed in a TV game show.

These are irritating distractions from Spoerli's choreography, which has some appealing features. His characteristic lines are lean, stretched and disciplined, yet they are punctuated by moments of unpredictable abandon when dancers skid joyfully on their own momentum and reinvent classical lifts with an acrobatic flourish. The choreography looks particularly good on Revie, who, with his clever, secretive face and dynamic intensity, is a figure of considerable charisma.

The ballet is, however, two hours long, and its length exposes its weaknesses cruelly. Spoerli may create interesting individual moves but they do little other than skim over the surface of the medley of Mozart's scores. There is no counter-argument in the dance's structure that would allow us to hear the music freshly, nor is there any emotional engagement with it. The steps just keep coming, regardless of what is being played.

Mozartina may flourish its lack of sentiment and clutter like a badge of modernity, but the fact that many of its devices are raided from ballets which were voguish a generation ago makes it look, actually, rather old-fashioned. It certainly doesn't look as if Spoerli created it because he had something urgent to say about the music or the subject. And without that urgency, an art form can never be renewed.

• English National Ballet's Sleeping Beauty is at the Royal Albert Hall, London SW7 (020-7589 8212), till Tuesday. The Kirov's Sleeping Beauty is in rep at the Royal Opera House, London WC2 (020-7304 4000), till August 10.