Ask that of John Bennett, whose Ski Independence has specialised in North American skiing holidays for the last five years, and he comes up with instant answers: for good service; uncrowded pistes ("It's said that when all the seats on all the chairlifts at Aspen's Snowmass mountain are filled, each skier will still have an acre of skiing to themselves once they get off"); guaranteed snow; good-value eating and drinking, and the wide variety of things to do apart from skiing. When prompted, he will add the fact that everyone over there speaks our language fairly well, too.
Nobody could argue about the service, but sometimes it would be nice if just one waitress admitted that she didn't really care how you are. Uncrowded pistes? Generally, yes - but what's true of Colorado's Beaver Creek (Bennett says: "The chances of hitting another skier there are infinitesimal") doesn't apply to Killington in Vermont on a busy weekend.
Guaranteed snow is fair enough, too, but there's a big difference between the real, powdery stuff in the West and the partly man-made snow that can switch between slush and ice and back again in the wildly fluctuating temperatures of the East Coast.
The good value in restaurants and bars is certainly a persuasive argument for North America, where - unlike France - standards don't necessarily drop at higher altitudes.
When it comes to the variety of things to do, Bennett was talking not only of British skiers' tendency to mix skiing with sightseeing (on popular combined packages such as Whistler with Vancouver, and Mammoth with San Francisco), but also about the wide range of in-resort activities.
He should, I think, put the common language higher on his list: skiers are generally gregarious and North America is almost the only winter- sports destination where Britons can sit in a bar or on a chair-lift and be sure to find themselves in conversation with their neighbours - except when the latter have flown in from Mexico, Brazil or Japan.
So what about the skiing? Perhaps Bennett didn't mention that, as it is difficult to generalise about North American resorts, this varies widely. Over the last few days I've heard a New Zealand photographer sing the praises of Taos in New Mexico for its desert setting, adobe architecture and wicked skiing; learned that Richard Branson's favourite resort is Mammoth in California, and been told that the average British skier chooses Whistler/Blackcomb in Canada and Breckenridge in Colorado above other North American resorts.
Add the epic Jackson Hole in Wyoming and the beautifully-designed Mont Tremblant in Quebec and you have an extraordinary range of types of skiing - but only the last has anything like the sort of ski village to which Europeans are happily habituated. Tremblant's is in fact a modern pastiche, artfully achieved. Many US resorts seem more closely modelled on motorway service stations. Alpine skiers also take mountains for granted, but they're in short supply in North America: despite many exceptions, the general rule is that you ski on high hills - often very high, up to 4000m - rather than on rugged, spiky peaks like those in the Alps.
But there are enough advantages to have doubled the number of British skiers going to North America in the mid-Nineties, a time when the weakness of both the US and Canadian dollars against the pound made a skiing trip across the Atlantic at least less expensive, if not exactly cheap. Since then the overall numbers have stabilised, the major recent development being the rapid growth of Canada against the US - a trend that now seems to be over, despite the low value of the Canadian dollar. The debacle of the 1997/8 season, when flight capacity to the Colorado resorts expanded way beyond demand, has made big operators more wary of the North American business. But the specialists - Bennett included - remain confident about the loyalty of the nine per cent of British skiers who ski there, even though the premium charged on what are already comparatively high prices seems to have hit transatlantic business over the millennium particularly hard.
Those specialists have the benefit of the huge range of resorts to keep their regular customers stimulated. Even this year, when most operators have been reluctant to launch new destinations due to the complications caused by the millennium calendar, Bennett has introduced Purgatory in Colorado, Deer Valley in Utah, and Sunday River in Maine to Ski Independence's 1999/2000 brochure. The first two are selling slowly; the third is going down a storm - both for him and for other operators, too.
Trying new resorts is an almost risk-free process for habitues of North America. They know that the resort won't be a charming ski village, that the skiing will be safe and somewhat sanitised, and that the lift queues will be organised with almost military precision. But they know, too, they'll get a great welcome. Not just as North American service personnel are good at that, but also as anyone who stays for a week (or more) is a highly valued customer. Most Americans get only a couple of weeks' holiday a year, so ski resorts have to compete not just with one another but with the Caribbean, with cruise liners and with Europe. That's why the facilities and services have to be so good. Ski in North America, and you get the benefit of that.