Keystone or Sun Valley?

Neither place is for a beach trip, but Sun Valley at least gives you somewhere natural to swim in high summer. Redfish Lake under the Sawtooths, about an hour north, has a sandy shore, and the Big Wood has river eddies closer to town, though the water is cold. At Keystone, Dillon Reservoir is for sailing and the view, not swimming, so a hotel pool or hot tub is the realistic way into the water.

Sun Valley eats better because it has a town attached. Ketchum has more restaurants than its size suggests, with serious kitchens cooking Idaho trout and elk, breakfast places that fill up on ski mornings, and patios and a farmers' market in summer.

Keystone's food is resort food: grills and pizza at the bases, craft beer at après-ski, and a dining room at the summit reached by gondola. Plenty of visitors cook in their condos or drive to Frisco or Breckenridge for more choice.

Sun Valley has a little more story to it. The 1936 lodge, built by the railroad as America's first destination ski resort with the first chairlifts, still has its corridors of film-star photographs. Hemingway's grave and memorial are in Ketchum, and a small history museum and art museum fill an afternoon.

Keystone is a 1970s ski resort with almost nothing to see on site. Its history lies in the mining ruins and old cabins up the Snake River valley and in the Victorian towns nearby.

Both wind down early, but in different ways. Keystone's evenings begin and largely end at River Run's après-ski decks, and anyone wanting a proper night out takes the bus to Breckenridge's Main Street. Sun Valley keeps its nights in town: Ketchum's saloons and wine bars sometimes have a band on winter weekends, and a couple of old western bars stay loud until closing time.

Both are first-rate mountain destinations, and the difference is in the kind of trip. Keystone is the place to ski several mountains in one week: its own three peaks with bowls above 3,600m, Arapahoe Basin a few minutes away, and Breckenridge, Copper and Vail within an hour. In summer, Grays and Torreys Peaks offer a 14,000ft summit close by.

Sun Valley is built around one big mountain. Bald Mountain's steep, uninterrupted fall-line runs are its signature, with Nordic trails and backcountry touring in the side valleys. Summer brings dense singletrack, fly fishing on the Big Wood and Silver Creek, the Sawtooths' alpine lakes and rafting on the Salmon.

Keystone is far better placed for days out. Breckenridge's Victorian centre is about half an hour away, the Georgetown loop railway and the old silver towns lie over the Divide, and Leadville and Vail are within reach. Denver's museums are a long drive away, but a possible one.

Around Sun Valley the land is wild, with few towns. Hailey's main street, the log cabins of Stanley and Shoshone Falls, about two hours south, are the main options. Most outings head into the mountains rather than to other places.

Keystone is made for family ski trips. It has a large ski school, tubing, a giant snow fort on the mountain and a frozen lake at Lakeside Village that turns into one of the country's largest outdoor rinks. Condos with kitchens and free shuttles make the logistics easier.

Sun Valley works well for families who already ski. Its separate beginners' hill keeps learners off the main mountain, and Ketchum's quiet streets are easy with children. Beyond that, there is little made just for children, and teenagers who don't ski may get bored.

Both work without a car once you are there, but in different ways. Keystone's bases are spread out and linked by shuttles, while free county buses reach Frisco, Dillon and Breckenridge, so your car-free range is wider. The catch is the drive from Denver over I-70, which can be slow in winter.

In Sun Valley, Ketchum's small, flat grid is easy to walk, and a bus and a valley-long bike path link it to the lifts. Trailheads, hot springs and the Sawtooths all need a car, though, and the local airport at Hailey is small.

Sun Valley is the better place to browse. Ketchum has fine art and western art galleries with evening gallery walks, well-stocked fly-fishing and outdoor shops, and boutiques selling cashmere and western wear. Keystone's own shops are mostly for gear and rentals, and its real draw is the outlet centre in Silverthorne for brand-name clothing and outdoor wear.

Both are expensive, and neither has a cheap season. Keystone is easier to manage on a budget: many condos have kitchens, the supermarkets in Dillon and Silverthorne make self-catering simple, and summer costs noticeably less. Sun Valley's prices are set by its wealthy second-home owners and there is little budget lodging. Staying further down the valley or visiting in the quiet spring and autumn months helps most.

Sun Valley's summer is the stronger draw. A full professional orchestra plays several weeks of free concerts in the pavilion by the lodge while people picnic on the lawn, and star figure skaters perform on the outdoor rink on summer evenings.

Keystone's summer music is spread around the area: village stages, Dillon's amphitheatre by the reservoir and Breckenridge's classical festival. It does have the edge out of season, though, thanks to the professional theatre company in Silverthorne.

Sun Valley is the more restful choice, mainly because of its natural hot springs. Up the Warm Springs valley, rough pools sit beside the creek at the end of a dirt road, and the resort adds full spas and steaming heated pools.

Keystone's wellness is about recovering after a day of skiing: resort spas and a hot tub at almost every lodge. For natural springs, you have to drive over the pass to Idaho Springs.