Moab or Sun Valley?

Neither town is anywhere near a coast, so the difference lies in where you can cool off. Moab has Mill Creek's shallow pools, Ken's Lake and the sandbars of a fast, silty Colorado River, so for most visitors swimming means the motel pool. Sun Valley's best option is Redfish Lake under the Sawtooths, which has a real sandy shore but cold water and is an hour's drive away. Its heated outdoor pools are the more reliable choice.

Sun Valley eats better. Ketchum supports a few serious kitchens cooking Idaho trout, lamb and elk for its second-home owners, and summer brings a farmers' market and patio dining.

Moab is about refuelling. Burgers, tacos, pizza and brewery food fill Main Street, with only a handful of ambitious Southwestern dinners. Utah's alcohol rules also make a glass of wine with dinner less relaxed than in Idaho.

Neither will fill more than a morning or an afternoon, but the history they offer is very different. Moab's is ancient: Ancestral Puebloan and Fremont petroglyphs on the cliffs along Potash Road and Kane Creek, and dinosaur trackways close to town.

Sun Valley's story is twentieth century. America's first destination ski resort and the world's first chairlifts date from 1936, the Lodge's corridors are lined with photographs of film stars, and Hemingway's grave lies in Ketchum's cemetery.

Both are early-to-bed towns without clubs. Moab's evenings are brewpub stories among rafters and bikers, and the best thing after dark is the star-filled desert sky. Ketchum's après-ski saloons, wine bars and hotel lounges are a little more polished and stay livelier in ski season, sometimes with a band on winter weekends.

The real choice here is red desert stone or green alpine valley, and either makes a superb base. Moab is all rock and canyon. Arches begins at the edge of town, Island in the Sky and Dead Horse Point look down into the gorges of the Colorado and Green rivers, and bikers come for Slickrock and the Whole Enchilada. Canyoneering, climbing at Wall Street and jeep trails fill the other days.

Sun Valley changes with the seasons. In winter Bald Mountain's steep runs come straight down into Ketchum, and in summer the same slopes become singletrack. Fly fishers work the Big Wood and Silver Creek, and the Sawtooth lakes and rafting on the Salmon are about an hour north. Early summer brings wildflowers and elk, and in autumn the aspens turn gold.

In both places the days out lead into wild country, not to other towns. From Moab the most rewarding outing is south into Ancestral Puebloan country, to Edge of the Cedars and Hovenweep, with pioneer Bluff on the way. Sun Valley offers historic Hailey nearby, log-cabin Stanley beyond the Sawtooths and Shoshone Falls two hours south.

Both work well for active families and poorly for toddlers. Moab's appeal is adventure: scrambling over rock to Sand Dune Arch, dinosaur tracks, calm river floats and Junior Ranger badges. On the downside, summer heat, unfenced drops and long drives make it harder with young children.

Sun Valley is gentler, with a separate beginners' hill and a good ski school, plus horse rides, an outdoor ice rink and quiet streets. Midwinter cold and altitude are its drawbacks, and teenagers who don't ski may get bored.

Sun Valley is far easier without a car. A free bus links Ketchum, the village and the lift bases, and a paved path runs the length of the valley, so many visitors spend a ski week without driving. You still need a car for the Sawtooths and the hot springs.

In Moab a car is essential from day one. Apart from Main Street and the bike path to the Arches entrance, everything is reached by long desert roads or dirt tracks. Without a vehicle, and ideally a high-clearance one, you depend on outfitters' shuttles.

Ketchum has more to browse. It has fine and western art galleries with evening gallery walks, fly-fishing shops and upmarket boutiques selling cashmere and western wear, though prices are high. Moab is practical: bike and climbing gear, rock shops full of geodes and fossils, and some Navajo jewellery and weavings.

Moab is the less expensive of the two, but only by comparison. Beds in a small town that fills up every spring and autumn cost a lot for what they are, and hire cars, fuel and paid outings such as rafting or jeep tours soon add up. Once you are there, though, most of what you came for costs very little, and a winter visit is far cheaper.

Sun Valley is costly at every step, from the room to dinner to the lift ticket, because the valley is priced for the people who own homes there rather than for visitors passing through. Basing yourself further south, using the free bus and avoiding ski season and midsummer all bring the bill down, but a stay here is always a splurge, while in Moab you can still plan a moderate trip.

Sun Valley has the stronger summer programme. A full professional orchestra plays weeks of free concerts in the pavilion by the Lodge while people picnic on the lawn, and star skaters perform on the outdoor rink in the evenings.

Moab has one remarkable event, the Moab Music Festival, whose chamber concerts are held in canyon grottoes reached by boat at the end of summer. For the rest of the year, live music means a brewpub band.

Sun Valley is much better for rest. It has full resort spas, steaming outdoor pools and the undeveloped hot springs beside the creek up Warm Springs, and its pace slows once the lifts close.

Moab has no hot springs worth the trip and only small massage studios for tired legs. Its restfulness comes from silence: dark skies and the cliffs turning red at dusk.