Fourth Plinth, National Gallery, London

Mirrors and meerkats fight the new battle of Trafalgar: Only two serious contenders are among the proposals for London's most famous empty site

Panned as it has been, I have a soft spot for Thomas Schütte's piece for the fourth plinth of Trafalgar Square, Hotel. Not on account of its formal qualities – Schütte's sculpture looks like the architect's model for a Hilton in Dubai – but of what it stands for. That Hotel feels like a maquette is precisely what it is about. It is a phase, not a work; a piece of speculative building, run up on the cheap and meant not to last. And its supposed end use – a place where travellers spend a night or two – is likewise fugitive. Trafalgar Square says all kinds of things about history and posterity and monumentalism. Schütte's work quietly points out that we do not live in an age of monuments.

This anti-monumental theme has, by and large, been the one followed by fourth plinth artists over the past nine years, and the latest round of submissions, by Jeremy Deller, Anish Kapoor, Tracey Emin, Yinka Shonibare, Antony Gormley and the fictive duo, Bob and Roberta Smith, does not buck the trend. In a place that celebrates national prowess at war, all but one of the artists have gone for works that subvert imperial might. This makes me sigh. We all know that imperialism is bad and artists good; Mark Wallinger made that point with State Britain. But how can any fourth plinth sculpture hope to compete as anti-establishment propaganda with the ones already there? The square's other plinths are occupied by statues of George IV, General Napier and Sir Henry Havelock. If you can tell me, without Googling, which were the battles won by these men, you should go on Mastermind. That Britannia no longer rules the waves, and that we no longer want her to, is most vividly proved by the fact that nobody gives a stuff about old generals. For all its marble and bronze, Trafalgar Square is a homage to forgetting, not war. In any case, Sir Charles Barry's unfinished pantheon was always proof that the British are bad at bombast. (Can you imagine the French leaving an empty plinth on the Place Vendôme?)

For Trafalgar Square to work as a site for letting off anti-imperialist squibs, it would have to be good at making pro-imperialist ones. If not, the joke falls flat. Jeremy Deller's submission, Spoils of War (Memorial for an unknown civilian) is the most annoying of the new proposals because the most self-satisfied. Playing on the classical tradition of showing military plunder back home, Deller suggests topping the fourth plinth with a burnt-out car from Iraq. How this would be recognisably different from the ones in my south London street is not clear.

Bob and Roberta Smith's zany confection of wind turbines and solar panels also plays the smug card, although the lightbulb-words illuminated by these are at least open to misinterpretation. Seen from the bottom of the square, the Smiths' sculpture would broadcast the inflammatory message faîtes la guerre; not its point, presumably. In Tracey Emin's Something for the Future, the meerkats' out-of-scale relation to the site rips off Mark Wallinger's more talented Ecce Homo. In times of national crisis, it seems, the British band together and make peeping noises. Dear God.

Antony Gormley's contribution is a fanfare to the common man that would see the plinth occupied, hour by hour, by members of the public. A safety net would prevent Gormley's living sculptures in One and Another from hurting themselves, which may say more about the state of modern Britain than he meant to.

And then there were two. As befits the playful Yinka Shonibare MBE, his Nelson's Ship in a Bottle is the only proposal that engages directly with British history. Fitting out the Victory with batik sails and bottling it deflates all kinds of painful issues, not least the slavery that paid for British conquest. Shonibare's work is thoughtful rather than strident.

Anish Kapoor, meanwhile, has done what he does and covered his plinth in round mirrors. Sky Plinth would thus bring the sky to earth which, as its maker remarks, is the ultimate in monumentalism. Neither of these works shows the artists at their best, but they are at least preferable to the silliness of the rest. We will have to live with the winning entry for 18 months. Pray that it is one of the last two.

National Gallery, London WC2 (020-7747 2885) to 30 March

Need to know

It is world famous as London's public heart, but Trafalgar square is a relative newcomer in the city's history. It was laid out by John Nash and Charles Barry and completed in 1845. At the corners of the square two plinths display military statues and a third hosts George IV. The fourth plinth, intended for William IV, was erected in 1841 and remained empty until 1999 when the current art scheme began.