PEOPLE SMILING on buses is an unnatural sight in Scotland. Especially when said bus is open-topped and the Scottish summer is coating the passengers with a fine film of drizzle. The reaction of Marilyn Ellis, a 70-year-old shivering and turning a shade of beetroot but grinning like a Cheshire cat, deepens the sense of unreality. "I feel like I'm in dreamland," she says. "I've wanted to come here for so long and never thought I'd get the chance." That's not the hypothermia talking; Ellis is from Colorado and is braving the elements on a bus tour of Edinburgh. Tourists definitely see things differently.

Ever since Dr Johnson and James Boswell took a package tour of the Hebrides in the 1700s, Scotland has attracted tourists like midges around a Highland millpond. Traditionally Edinburgh's handsome Georgian facades, dark, knotted Old Town and blockbusting castle draw the most visitors. But a recent report suggests that Glasgow, having proclaimed for years that it was miles better, is now neck and neck. For the first five months of this year hotel occupancy in both cities was 73%.

But what do visitors actually see when they come here: and does Edinburgh or Glasgow offer the best experience? In an effort to live the Caledonian dream so vividly evoked by Marilyn Ellis, I am spending one day in a corner of Scotland that will remain forever foreign: the city tour bus, on board which the only Scots are the driver and the guide.

First stop, Edinburgh. On the top deck, our amiable tour guide Graham Morton is wiping down the rain-drizzled seats with his wife's best dishcloth. Before starting this job three years ago, his view of tourists was somewhat jaundiced. "They were a bloody nuisance," he says. "You couldn't get on the bus because of them, you couldn't get past them on the pavements. Now they give me a round of applause. It's good for the ego. I sat in a bank for 20 years and no-one clapped when I cashed a cheque."

During the hour-long journey, the passengers are held captive by Morton's light-hearted banter ("From half-a-mile away the parliament building doesn't look too bad. It looks even better from 10"), his commentary on the Old and New Town's most notable buildings, and some well-rehearsed tales of the characters who make Edinburgh's history so alluring: witches and kings, Burke and Hare, Adam and Miralles.

The passengers are a stereotypical mix of midwestern Americans and snap-happy Japanese tourists, gazing at "the most famous castle in the world".

Stella, who is from central Greece, sits at the front of the top deck, wrapped up against the elements. Her English friends brought her to Edinburgh because she wanted to come to Scotland and they recommended the capital above everything else. "It's a beautiful city," she says, as we pass the doric columns of the National Monument on Calton Hill. "The buildings are very much influenced by back home."

Is she aware of Edinburgh's reputation as the Athens of the north? "Ha!" she laughs. "I think this has nothing to do with the weather."

Three of Edinburgh's four bus tours - including this one - concentrate on the Old and New Towns. The next one I try takes a less well-trodden tourist path to Leith. This time, there is a pre-recorded audio tour-guide voiced by a Scot who sounds uncannily like Sean Connery. As we pass through the less salubrious parts of Leith, gentle folk music plays over the tannoy, a musical balm to help soothe the prospect of looking at the notorious banana flats. Sadly, no mention is made of Trainspotting, Irvine Welsh, or even the Port O'Leith pub, one of the city's greatest hang-outs, whose karaoke night has more colour and noise than the Rio carnival, and more broken crockery than a Greek wedding.

On the lower deck, Malcolm and Christine Broad from Solihull are sheltering from the cold. Asked if they plan to visit Edinburgh's west coast counterpart, they look slightly shocked.

"Glasgow? Oh, no," says Christine. "It's Edinburgh. Always Edinburgh."

"I've been to Glasgow on business and I don't think so," adds Malcolm, knowingly. "Certainly not on holiday. But I hear it's revived itself."

Graham Morton doesn't seem worried about Glasgow stealing Edinburgh's tourism crown. "But it's still a very attractive city," he admits. "It's marketing itself really well. Only a couple of years ago the perception of Glasgow was that it was a dump: go there and you'll get knifed. Not any more."

A few hours later, on the top deck of a tour bus in that very city, Michelle Anglin from Miami, sitting on the back seat, happily obliterating our friend in the east from the tourist map of Scotland. "Edinburgh? Nope, never heard of there. We just wanted to come to Glasgow.

"Oh, Edin-berg!," she corrects, finally overcoming the gulf of our shared language. "Yeah, we're going there, but spending most time here."

"We were told that Glasgow was up and coming, so that's why we're here," explains her mother, Marcia. "We're from Kingston, Jamaica originally and this reminds me of there - the way the city was laid out. It used to be a British colony too."

Sadly, this tour bus doesn't cross the bridge named after her hometown nor even down the street named after her native country, but the Second City Of The Empire does a fine job showcasing what the fat of her land brought to Glasgow. Travelling along Glassford Street in the Merchant City is like being in an architectural zoetrope as the ornate masonry, invisible at pavement level, whizzes by.

"There's a different form of tourism in Glasgow, it's more to do with corporate, business and conferences," says Alex Pringle, director of City Sightseeing Glasgow. When bus tours began here in 1993, 10,000 souls did the loop between two of the city's dear green places: Glasgow Green in the east, Kelvingrove Park in the west. Last year that figure was 150,000. "Still, Edinburgh takes 350,000 a year," adds Pringle. "In Edinburgh all the tourists have big Ts on their foreheads. You don't come to Glasgow for haggis, kilts and castles. You come here for wine bars, good food, culture and architecture."

And it's the latter that forms the backbone of Glasgow's tour, which eschews the more kilty pleasures associated with Edinburgh. The bus lingers around Kelvingrove Art Gallery and Museum, Glasgow University and the Armadillo, like an infatuated lover, allowing us to take in all these buildings' curves, dips, light and shade. They may not be as iconic as Edinburgh castle, but these architectural treasures cut a graceful silhouette against the skyline. However, in the vernacular of Malcolm Gould, our Bill Nighy lookalike tour guide, most of the architecture in Glasgow appears to be about conversion, rather than building.

"Everything seems to have been converted into flats," agrees Ray Hart from Vancouver, Canada, in a voice that conveys both wonder and sadness. Indeed, at times the tour feels like a trip around the city's new apartment blocks. Hart was born in Scotland and lived on Glasgow's outskirts before emigrating in his early 20s to work in the hot tub business in British Columbia. "Not many hot tubs here," he remarks. "We're interested in seeing how it's changed. It's definitely becoming more of a destination now. You hear more about it in papers back home, about it being a city of culture. We're looking forward to seeing the shops and modern buildings. And the new flats."

Where Edinburgh's tours shy away from mentioning anything constructed within the last 100 years, Glasgow's big on new-build. Why else would we be spending 10 minutes circumnavigating the car parks around the Scottish Exhibition and Conference Centre, instead of admiring the famous traffic cone that is permanently perched atop the Duke of Wellington statue outside the Gallery of Modern Art? Perhaps gallus is giving way to commerce as a pull in this city.

For the most part, citizens of these two great cities appear to consider their local tourist attractions as they would the "good rooms" of their home. They are kept nice and tidy, house the most expensive items, yet are only really used on special occasions or when visitors call. Usually they are too busy with life to step across the threshold.

The attitude towards the "other" city, meanwhile, tends to be unkind at best. In the west, Edinburgh is cast as a Fabergé egg of a place, beautiful but heartless, while in the east Glasgow is seen as a deep-fried industrial sink-hole.

And then you sit on a tour bus in front of people like Cory Lynn, a retired tour operator from New York. "Glasgow's a beautiful city! The architecture here is phenomenal. The variety is amazing!" This is Lynn's second loop of the city tour bus today. He is staying on for one more. "I've travelled all over the world. And while Prague is probably the most beautiful city I've seen, this is impressive too.

''Rick Steves' America's travel oracle - a star-spangled Judith Chalmers guide book said Glasgow is just a one-night place. I don't understand that. It says Edinburgh is more beautiful, but this is amazing. I'm going to write to Rick Steves when I get home."

As he says this, we pass the grim Buchanan bus station, before driving through the shadow of some stark high rise flats. He sounds so sincere, you just have to smile. Even in the summer rain.