San Francisco or Sun Valley?

Neither city is a beach destination, though San Francisco at least has a shoreline worth visiting. Ocean Beach and Baker Beach, with the Golden Gate in view, are good for sunset walks and bonfires, but the cold Pacific and rip currents keep most people out of the water.

Sun Valley is hundreds of kilometres from the sea. Its summer swimming means cold mountain water at Redfish Lake, an hour north, or the heated outdoor pools, which are the warmest swim either place offers.

San Francisco is one of the reasons people cross the country to eat. Bay seafood, sourdough, cioppino, Chinatown's Cantonese kitchens, North Beach bakeries, Mission taquerias and a top fine-dining tier sit on top of Northern California's produce and wine.

Ketchum feeds a ski resort well enough, with après-ski grills, a few ambitious kitchens doing Idaho trout and elk, and a summer farmers' market. There is no local cuisine to seek out, though, and some places shorten their hours in the quiet seasons.

San Francisco gives a visitor three or four full days of sightseeing: Alcatraz, the cable cars on Nob Hill, the painted Victorians at Alamo Square, and museums from SFMOMA to the Legion of Honor, plus the murals of the Mission and the Castro's history.

Sun Valley's story fits into an afternoon. Union Pacific's 1936 resort with the first chairlifts, the film-star photographs in the lodge and Hemingway's grave in Ketchum are interesting, but they are worth a short visit rather than a reason to come.

A night out in San Francisco has real choice across districts: mezcal and cocktail bars in the Mission, old saloons in North Beach, the Castro's gay bars and SoMa's warehouse clubs. It winds down at 2am and can be quiet midweek.

Sun Valley's evenings mean après-ski in a few Ketchum saloons and hotel lounges, perhaps with a band on a winter weekend. There are no clubs, and out of season most nights end soon after dinner.

Both have superb surroundings, but Sun Valley is built entirely around them. Bald Mountain rises straight out of Ketchum for steep skiing, and summer brings singletrack, the Sawtooths' alpine lakes, fly fishing at Silver Creek and rafting on the Salmon River, real wild country an hour away.

San Francisco's nature is coastal and close at hand: the Lands End cliff trail, Golden Gate Park, the Marin Headlands across the bridge, the redwoods at Muir Woods and the elephant seals at Point Reyes. It is excellent for day hikes from a city base, but has no snow and no mountain range.

San Francisco has the stronger region for day trips. Napa and Sonoma's wineries, ferries to Sausalito, Berkeley's campus, and the coast down to Santa Cruz, Monterey and Carmel give a week of easy outings.

From Sun Valley, most trips go into the mountains rather than to towns. Hailey's main street and log-cabin Stanley are pleasant stops, and Shoshone Falls is a long drive south, but there is little else to tour.

San Francisco has more for children to see and do: the Exploratorium, the aquarium and planetarium at the California Academy of Sciences, sea lions at Fisherman's Wharf and cable car rides. The steep hills with a pushchair and some rough downtown streets are the drawbacks.

Sun Valley suits families who ski or hike, with a gentle beginner hill, a good ski school and quiet, safe streets. Nothing is built for children, though, rainy days are hard to fill, and the cold and altitude can be tough on toddlers.

San Francisco runs fine without a car: BART, Muni, the cable cars and the bay ferries all take one Clipper card, though the hills turn short walks into climbs.

Sun Valley is simple only inside the resort, where Ketchum is walkable and a free bus links the village and lift bases. For the Sawtooths, trailheads or hot springs you need a car, often on snowy winter roads.

This is broad big-city range against a few blocks of galleries and gear shops, and San Francisco wins easily. Past the department stores of Union Square, the best browsing is in independent fashion, bookshops and vintage spread across several neighbourhoods, and tea or ceramics from Grant Avenue make better souvenirs than anything from a flagship.

Ketchum's shops cater to skiers, anglers and second-home owners. That makes it a good place to buy ski kit or a fly rod, with western art and cashmere at high prices beside them, but there is not enough to fill a day of shopping.

Both are expensive, and neither suits a tight budget. In San Francisco, cheap meals are easy to find, from Mission taquerias to dim sum in the Richmond, and the parks, coastal trails and bridge walk cost nothing.

Sun Valley's prices are set by its wealthy second-home owners, and budget lodging barely exists. The savings there come from timing and location instead: visit in spring or autumn, stay down the valley and use the free buses.

The difference is between a whole year of performances and one short summer season. San Francisco has full seasons of opera, ballet and symphony at the Civic Center, serious drama and touring musicals downtown, and live music from a dedicated jazz hall to the Fillmore's psychedelic-era stage. Whatever week you arrive, there is a choice of evenings.

Sun Valley's performances come almost entirely in summer. A professional orchestra plays several weeks of free concerts in the pavilion by the lodge while people picnic on the lawn, and star skaters perform on the outdoor rink. Come in the ski season and there is little beyond the odd band in a bar.

Sun Valley is the easier place to unwind. Its slow pace after the lifts close, the hotel spas, the outdoor pools steaming in the snow and the rough creekside hot springs up Warm Springs valley make rest part of the stay.

San Francisco's centre feels busier and work-driven. Its quiet spots are the Japantown bathhouse, the Japanese Tea Garden and the day spas, and Calistoga's mud baths are a two-hour drive away.