Key West or St. Petersburg, Florida?

St. Petersburg is the place for beaches in the usual sense. St. Pete Beach and Pass-a-Grille have wide, fine white sand, Fort De Soto is wilder, and Clearwater and Caladesi Island are a short way north. The catch is that downtown faces the bay, so every beach day starts with a short trip west.

Key West's own beaches are small, with imported sand at Smathers and coral rubble at Fort Zachary Taylor. The island is better for snorkelling from a boat than for lying on a towel. Its one advantage is the winter sea, which stays warm enough to swim when St. Petersburg's Gulf is only good for a paddle.

Both cities eat mainly seafood in casual places by the water, but St. Petersburg has more range. Central Avenue has modern American kitchens and a few chef-led dining rooms, there are craft breweries all over the city, and Ybor City's Cuban and Spanish cooking is just across the bay. Key West's food is narrower and more local: conch fritters, pink shrimp, Key lime pie and Cuban coffee from takeaway windows. Much of Duval Street serves bar food at resort prices.

St. Petersburg has the stronger museums. The Dalí Museum on the waterfront leads, with the Museum of Fine Arts, the Chihuly glass collection and the James Museum of Western art close by.

In Key West the main sight is the town itself: Old Town's streets of conch cottages and Victorian verandas. Its museums are small houses with a story, such as Hemingway's home with its six-toed cats and Truman's Little White House. Go to St. Petersburg for galleries and to Key West for walking among old wooden houses.

Small as it is, Key West has the bigger night out. Open-sided bars and old saloons run the length of Duval Street, you carry your drink from one to the next, and the night goes on into the small hours. There is also a long-established gay scene at the upper end of the street. It is loud and boozy rather than stylish.

Evenings in St. Petersburg are calmer. They centre on the cocktail bars, rooftop terraces and brewery taprooms along Central Avenue, plus tiki bars on the beaches. For a rowdier night, people cross to Ybor City in Tampa.

Both are flat landscapes shaped by water, with no real hiking, but the water offers different things. Key West sits beside the Florida Reef, with snorkelling and diving boats leaving daily. It also has backcountry flats for tarpon and bonefish, and the remote Dry Tortugas.

St. Petersburg is better for paddling through mangroves at Weedon Island and Shell Key, where manatees appear in winter. It also has good birdwatching at Fort De Soto and long bike rides on the Pinellas Trail.

St. Petersburg is much better placed for day trips. Ybor City in Tampa, the Ringling in Sarasota and the Greek sponge docks of Tarpon Springs each make a different kind of outing, and Orlando is possible as a long day.

Key West sits at the end of the road. The ferry to Fort Jefferson in the Dry Tortugas makes a memorable day, and the drive over the Seven Mile Bridge to Marathon is pleasant. After that, the options run out quickly.

St. Petersburg is the easier family choice. It has gentle, shallow Gulf beaches, resorts geared to children and a hands-on children's museum. The Clearwater Marine Aquarium is nearby, and Busch Gardens and ZooTampa are across the bay.

Key West can work for children who love the water, with glass-bottom boats, calm shallows at Fort Zachary Taylor and the Hemingway cats. But the drinking on Duval Street and adult festivals such as Fantasy Fest set the tone in the centre.

Key West is far simpler without a car. Old Town is flat and compact, bikes and electric carts are the local way to get about, and most of what you came for is a short walk from Duval Street. You only need wheels to go up the Keys.

Downtown St. Petersburg is easy on foot, and a trolley and a rapid bus line to St. Pete Beach cover the basics. The other beaches, Tampa and every day trip are really car journeys, though.

Neither city is worth visiting for the shopping, but St. Petersburg has more to browse. The Grand Central District has vintage and record shops, local boutiques and glass galleries, there is a Saturday market in winter, and Tampa's malls are half an hour away. Key West sells mostly T-shirts and Key lime soap along Duval. Its saving graces are the art galleries in Old Town and the hand-rolled cigars.

Neither city is cheap, but Key West costs noticeably more. Land is scarce so rooms are expensive, Duval Street charges resort prices, and boat trips and the Dry Tortugas ferry add up fast. Its one real saving is that you can walk or cycle everywhere.

St. Petersburg is cheaper to sleep and eat in, especially if you stay downtown or a little inland. A hire car and beach parking take back some of that saving. Both cities are cheapest in the hot, stormy summer months.

There is about as much to see in each, but it is different in kind. Key West's performance is informal: cover bands and singer-songwriters in the Duval Street bars, nightly drag cabaret, and the jugglers and tightrope walkers who play to the sunset crowd on Mallory Square.

St. Petersburg leans towards concert halls and theatres. The Florida Orchestra and touring shows play at the Mahaffey Theater, there is a regional theatre company, and Tampa's large arts centre is close by for opera and ballet.

Both offer resort spas and yoga rather than any bathing tradition, and both build the day around sunset. They differ in where you find quiet. In Key West it comes from guesthouse pools and gardens on Old Town's back lanes, though the parties are never far away. In St. Petersburg it means sleepy Pass-a-Grille and the waterfront parks downtown, at their most restful in the drier, less humid winter.