Islamorada or Sanibel?

This is where the two differ most, and Sanibel wins easily. Nearly its whole Gulf-facing shore is sand with little surf. People come for the shelling, walking the tideline at Bowman's Beach or Lighthouse Beach, and stay for the sunsets at Blind Pass and on Captiva. Bear in mind that its winter sea is noticeably cooler, and red tide can close beaches in some years.

Islamorada has warm, shallow water but very little sand. Anne's Beach and the small highway parks are narrow strips where you wade a long way out. Its best answer is the Whale Harbor sandbar, reached by boat, or a drive of about an hour to Bahia Honda.

The two eat much the same way, simple seafood in casual settings, but Islamorada does it better. Snapper, hogfish and mahi-mahi come in off the boats the same day, many waterfront kitchens will cook your own catch, and there are smoked fish dip, raw bars, some Cuban and Caribbean cooking and a few local breweries, mostly eaten on decks over the water.

Sanibel's grouper sandwiches and shrimp on the porches along Periwinkle Way are pleasant, but the menus repeat each other, and for anything more ambitious people drive to Fort Myers or Naples.

Neither island is worth visiting for its sights, but Sanibel's are easier to see and more distinctive. The Bailey-Matthews National Shell Museum is unlike any other in the country, and the 1884 iron lighthouse and the pioneer village fill a tidy morning.

Islamorada has more history but less to see. The History of Diving Museum and the 1935 Hurricane Monument tell a vivid story, while the wrecking ruins on Indian Key and the hardwood forest on Lignumvitae Key take a kayak or boat to reach.

Both islands go quiet early, but Islamorada has a bit more going on. Its open-air tiki bars and dockside decks along the highway fill up at sunset with fishing crews, rum drinks and, at weekends, a louder boating crowd. On Sanibel the evening is sunset, dinner and bed, with a few cheerful restaurant bars on Captiva the only exception. For anything late, it's Key West from one and Fort Myers from the other.

Islamorada is the richer choice, especially for anything in or on the water. The Florida Bay flats are classic water for bonefish, tarpon and permit, Alligator Reef gives clear-water diving, and the bay side leads by boat into the Everglades backcountry.

Sanibel's nature is about wildlife you can watch. The Ding Darling refuge brings roseate spoonbills, pelicans and alligators close on its Wildlife Drive, and Tarpon Bay's mangrove tunnels are lovely by kayak. Neither island has any hills, so walking on both is limited to flat paths and short trails.

Islamorada has the stronger single outing: Key West, about two hours south across the Seven Mile Bridge, with the Turtle Hospital in Marathon on the way. Key Largo is close by, and Miami can be reached in a long day. Still, with only one road, you get about one trip in each direction.

From Sanibel, the outings are gentler and closer: Captiva over a short bridge, the Edison and Ford Winter Estates in Fort Myers and Naples to the south. Its best trips go by boat, to Cabbage Key and the empty beaches of Cayo Costa.

Islamorada's family appeal is mostly about animals and boats. Feeding the huge tarpon at the docks is a reliable hit, Theater of the Sea puts on sea lion and dolphin shows, and a glass-bottom boat or a snorkel trip at Pennekamp lets children see the reef. Between outings there are the warm flats for paddling and the resort pools, but little else on the islands is made with children in mind, and most of the good days start with a booked trip.

Sanibel comes out ahead because the island itself keeps children busy without much planning. A morning on the refuge's Wildlife Drive brings alligators and spoonbills into view from the car, and a kayak on Tarpon Bay often turns up dolphins. The island is small, so the beach and the refuge are never far from a rented cottage or condo with room for everyone. The trade-off is that the days are simple and much alike, so it suits families who are happy with an easy, repetitive week.

You need a car on both, and neither has a bus worth relying on, but the layout differs. Islamorada stretches for about 30km along a single highway, so you drive between stops, ride the Heritage Trail now and then, and reach much of what you came for by boat.

Sanibel is compact and completely flat, so once you have crossed the causeway, cycling the shared-use paths between beaches and the refuge is the nicest way around. Its weak point is the high-season queue on Periwinkle Way.

Neither is for serious shopping, but Sanibel offers a little more browsing. The plazas on Periwinkle Way and in Captiva village have resort-clothing boutiques, shell shops and galleries of coastal art and jewellery. In Islamorada the landmark is a big sporting outfitter for tackle and outdoor gear, plus an artisan village and the roadside T-shirt shops.

Both are expensive, and in winter neither has a real budget option. The costs fall differently, though. In Islamorada the activities push up the bill, since charters, boat rentals and dive trips are the reason to go, and summer brings some relief. On Sanibel the beaches and bike paths are close to free, but beds are scarce, there are no budget hotels, and staying in Fort Myers is the usual way to save.

Sanibel has the small edge here. In winter its community scene puts on chamber concerts, talks and touring or amateur theatre, and the performing arts hall in Fort Myers is a short drive away. In Islamorada, live entertainment means a guitarist playing covers on a tiki deck, and any proper show is a long drive to Miami or Key West.

The two are evenly matched: both are restful because they are slow, not because of any bathing tradition, and on both the larger resorts have full spas. The difference is the kind of day. In Islamorada that means sunrise yoga on a dock and early starts on the water, while Sanibel offers tide-paced beach days with no high-rises in sight and a few independent massage and yoga studios.