Marathon or Sanibel?

On Marathon the sea matters more than the sand. Sombrero Beach is a pleasant palm-lined strip with clear water, but the Keys' reef-sheltered shores are mostly narrow, and the best sand is at Bahia Honda, twenty minutes away across the Seven Mile Bridge. Many visitors swim best from a boat over the reef.

Sanibel's whole Gulf shore is beach, gently shelving and calm, and walking the tideline for shells is a pastime in its own right. The water is greener and, in winter, much cooler than Marathon's, and red tide sometimes closes the shore. For days spent on the sand, though, Sanibel is the better island.

Both islands eat seafood in casual places, and neither has much fine dining. Marathon has the edge because its fish comes straight off the boats to marina-side tables: blackened mahi and grouper, conch fritters, Keys pink shrimp, spiny lobster in season, and fish markets that will cook your own catch.

Sanibel's porch cafés and breakfast spots along Periwinkle Way serve grouper sandwiches and stone crab, but the menus repeat each other. Anyone after variety drives to Fort Myers or Naples.

Neither island is a place for sightseeing, and both can be covered in a morning. Sanibel has slightly more to see. The Bailey-Matthews National Shell Museum has no equal anywhere in the country, and the 1884 iron lighthouse and the pioneer village add some local history.

Marathon's story is Flagler's Overseas Railroad, told through the workers' cottages on Pigeon Key and the old bridge beside the highway, with Crane Point covering early settlers. For old streets and bigger museums, both send visitors elsewhere, Marathon to Key West and Sanibel to Fort Myers and Naples.

Sunset is the main event on both islands, but Marathon has a little more going on afterwards. Its open-air waterfront bars and tiki bars stay sociable for a while with a crowd of boaters and anglers, and Duval Street in Key West is an hour's drive for a proper night out.

Sanibel is quieter still. Dinner follows the sunset, a few restaurant bars on Captiva have a guitarist in winter, and the island has gone to bed well before midnight.

Marathon's outdoors is the sea itself. Sombrero Reef in the National Marine Sanctuary has corals, parrotfish and turtles, the flats are known worldwide for bonefish and tarpon, and charters run offshore for sailfish. Add mangrove paddling at Curry Hammock, the Overseas Heritage Trail by bike and Key deer on Big Pine Key, and there is more to fill active days.

Sanibel is about wildlife watching. The Ding Darling refuge puts spoonbills, pelicans and alligators beside the Wildlife Drive, and the mangrove tunnels of Tarpon Bay often bring dolphins alongside a kayak. It is rich but gentle, and there is no reef to dive.

The two are about even for outings, but the shape differs. From Marathon everything runs along one road. Key West, with its conch houses, Hemingway's home and Mallory Square, is the one great outing, and Islamorada's diving museum and waterfront are the other. Beyond those two the choice runs out.

From Sanibel, outings spread over land and water: the Edison and Ford Winter Estates in Fort Myers, Naples' polished old town, and boat trips across Pine Island Sound to Cabbage Key, the empty beaches of Cayo Costa or Boca Grande. There are more options, though none has the pull of Key West.

Sanibel is the easier island for a family. Shallow, calm water runs along every beach, shelling absorbs children for hours, the flat paths are safe for small cyclists, and the shell museum's touch tanks are made for curious children. Teenagers may tire of it after a few days.

Marathon suits children who love animals. The Turtle Hospital and the Dolphin Research Center on Grassy Key are real highlights, and Sombrero Beach is gentle. But the attractions are spread along ten miles of highway, so more of the day is spent in the car.

A car is all but essential on both, and neither has public transport a visitor can rely on. Marathon is slightly easier to manage once there. The single highway is impossible to get lost on, a bike path follows much of it, and the marinas make boats the natural way to reach the reef and the backcountry. The catch is the long drive down from Miami, which a single accident can block.

Sanibel is small and flat, so cycling between beaches and the refuge is a pleasure. In the winter season, though, traffic backs up on Periwinkle Way and at the causeway, and the beach car parks fill early.

Nobody comes to either island to shop, but Sanibel has more to browse. Shell shops, resort-wear boutiques and galleries of coastal art and jewellery fill small plazas along Periwinkle Way and in Captiva village, enough for a rainy afternoon.

Marathon's shops are practical, mostly tackle, dive gear and T-shirts along the highway, and Key West's old town is the nearest place with real choice.

Both are expensive, especially from midwinter to April. The costs show up in different places. On Marathon the bill is driven by what you do, with fishing charters, dive trips and boat hire adding up quickly on top of resort-priced rooms.

Sanibel has no budget hotels at all, and height limits keep beds scarce, so lodging is the main cost. Staying on the mainland in Fort Myers is a real way to save there, while on Marathon a self-catering rental and the free beaches are the main ways to save.

Sanibel has a small but real winter season of chamber concerts, talks and touring theatre, and the performing arts hall in Fort Myers is a short drive for Broadway tours and bigger concerts. Marathon offers a community theatre and guitarists playing to the sunset crowd, with Key West, an hour away, the nearest place for more.

Both islands restore you through their pace rather than any spa culture, with days set by tides and sunsets and no thermal springs or retreats. Sanibel has more choice, with full-service spas at the larger resorts on Sanibel and Captiva and some independent yoga studios. Marathon's spa options are mostly massages at waterfront resorts, and its calm comes from doing very little by the water.