Marathon or Siesta Key?

Siesta Key wins on beaches outright. Siesta Beach is wide, made of white quartz sand that stays cool underfoot, and runs into shallow, calm Gulf water. Crescent Beach adds snorkelling at Point of Rocks, and Turtle Beach is the place for shell and shark-tooth hunting.

Marathon's shores are narrow and reef-sheltered, sometimes edged with seagrass. Sombrero Beach is pleasant for an afternoon, and the island's best sand is at Bahia Honda, across the Seven Mile Bridge. Here the sea itself is the attraction, and many visitors do their best swimming off a boat over the reef.

Neither is a place to travel to for food, and both live on Gulf and reef seafood eaten casually by the water. Marathon is closer to the source. Fish comes straight off the boats, there are conch fritters and Keys pink shrimp, and some fish markets will cook what you caught.

Siesta Key's own food is beach food: grouper sandwiches and fish tacos around Siesta Village. Its advantage is Sarasota, twenty minutes away, where downtown and St Armands Circle offer the international cooking and serious dinners that Marathon lacks.

Siesta Key has more to offer here, but only because Sarasota lies across the bridge. The Ringling estate alone, with its Rubens canvases, the Venetian Gothic Ca' d'Zan and the circus museum, fills a rewarding day. Selby Gardens and the mid-century modern houses of the Sarasota School add more.

Marathon's heritage is one story, Flagler's Overseas Railroad. It is told in the workers' cottages on Pigeon Key and the old bridge beside the highway, with Crane Point covering pioneer life. For architecture and museums you have to drive an hour to Key West.

Siesta Village gives Siesta Key a modest but real evening scene. A few blocks of open-air bars have cover bands and frozen cocktails, and it gets noisy at spring break, while downtown Sarasota has rooftops for a quieter drink.

In Marathon the evening ends soon after sunset. Tiki bars and marina hangouts fill with anglers and boaters who are up before dawn, and the nearest real night out is on Duval Street in Key West, an hour's drive away.

Marathon is the stronger outdoor base, and its best nature is under the water. Sombrero Reef lies in the Florida Keys National Marine Sanctuary, and the fishing, from bonefish and tarpon on the flats to sailfish offshore, draws people from far away. Mangrove paddling at Curry Hammock, the Overseas Heritage Trail and the Key deer on Big Pine fill the rest.

Siesta Key's nature is about wildlife you can see from the shore and the shallows: dolphins off the beach, manatees in the cooler months and nesting turtles in summer. Its best outings are the mangrove tunnels of Lido Key and the alligators and canopy walkway at Myakka River State Park.

Siesta Key has the wider range of outings because the Gulf coast opens in both directions. St Petersburg, with the Dalí Museum, is about an hour north, and Tampa's Ybor City, Anna Maria Island, Venice and Boca Grande are all within reach.

From Marathon there is one road and two directions. Key West is the obvious day out and a good one, with Islamorada's fishing village to the north-east, but after that the options run out quickly.

Both work with children, but Siesta Key is easier for a beach vacation. The main beach slopes so gently that toddlers can paddle far out, there are lifeguards, a playground and showers, and condos with pools make long stays simple. Mote Marine Aquarium on Lido Key is the main outing away from the sand.

Marathon's strength is animals. Children can watch sea turtles being treated at the Turtle Hospital and meet dolphins at the Dolphin Research Center, and glass-bottom boats and fishing fill the other days. Its beaches are smaller, though, and every outing means a drive.

Marathon is the simpler place to get around once you have arrived. Everything lies along one highway with a bike path beside much of it, distances are short, and the reef and flats are reached from the many marinas. The catch is the long drive down from Miami, and you will need a car on the island.

On Siesta Key the island itself is easy, with a walkable village and the free trolley running to Turtle Beach. Anything beyond the beach means crossing one of two bridges, and in the winter season those bridges jam and beach car parks fill early.

Siesta Key offers far better browsing, though still not enough to plan a trip around. Siesta Village covers swimwear and gifts, while St Armands Circle has upscale boutiques and jewellers, and Sarasota's Main Street adds galleries and bookshops.

Shopping in Marathon means fishing tackle, dive gear and T-shirt shops along the highway, with Key West's old town an hour away for anything more.

Both are expensive in their winter season, and the difference lies in where the money goes. In Marathon the stay is costly from December, and the charters, dive trips and boat rentals that are the point of coming add up quickly.

On Siesta Key the main cost is a beachfront condo from January to April. Once that is paid for, the beach and the island trolley are free, so a vacation spent on the sand costs less day to day than one spent on the water in the Keys.

Siesta Key comes out far ahead thanks to Sarasota, which has an arts life well beyond its size. There is a resident opera company in a restored 1920s opera house, the Asolo Repertory Theatre at the Ringling, a ballet company, a symphony orchestra and touring shows at the Van Wezel. All of it is busiest from autumn to spring.

In Marathon, live performance means a small community theatre and a guitarist at a sunset bar. Even the Sunday drum circle on Siesta Beach is more of an event.

Neither has any spa culture, and both relax you through their pace rather than their facilities. In Marathon the days follow the tides and the boats, and massages are found mostly at the larger waterfront resorts.

Siesta Key's version is built around the beach. There are morning walks on cool sand, beach yoga classes and long, quiet afternoons at the southern end around Crescent and Turtle beaches.