Key Largo or Marathon?

Neither island has the long sandy shore people picture in Florida, but Marathon comes much closer. Sombrero Beach is a proper palm-lined public beach in town, Curry Hammock State Park adds a quieter one, and Bahia Honda, across the Seven Mile Bridge, has the pale sand and clear water the Keys are known for.

Key Largo is built on fossil coral and has almost none of this. Swimming there means a man-made patch of sand at Pennekamp, a town park or a resort lagoon edged with seagrass. On both islands the sea is the same warm, calm water, and the best swimming of all is off a boat over the reef.

The menus are almost the same: grouper and mahi grilled or blackened, conch fritters, stone crab in winter and Key lime pie, eaten at casual tables by the water. Marathon adds Keys pink shrimp and spiny lobster, and some of its fish markets will cook your own catch, which suits a fishing trip.

Key Largo's advantage is its location rather than its cooking. It has a few more polished resort dining rooms, and Miami's restaurants are within driving distance when the seafood starts to feel repetitive.

Key Largo's sights are a few curiosities rather than a history. The boat from The African Queen is kept at a marina, and the bronze Christ of the Abyss lies on the reef, so you need a mask to see it. The nearest real museum is the History of Diving Museum, a drive south in Islamorada.

Marathon has an actual story behind it, Flagler's Overseas Railroad. On Pigeon Key, beneath the old Seven Mile Bridge, the workers' wooden cottages still stand beside a modest museum. Crane Point adds a restored pioneer house and the natural history of the islands, which together make a worthwhile half-day.

Evenings look much the same on both islands: a drink at an open-air bar as the sun goes down over the water, then an early night before the boats leave. Key Largo's bay-side tiki bars often have a guitarist and stay open later at weekends. Marathon's marina bars fill with anglers and boaters.

The real difference is where you go for a bigger night. From Marathon, Duval Street in Key West is about an hour's drive. From Key Largo, a proper night out means the drive north to Miami.

Both islands are flat limestone and mangrove and are really about the water, but Key Largo's reef is the bigger draw. John Pennekamp protects a long stretch of the only living barrier reef in the continental United States, with easy shallow sites for snorkellers and the Spiegel Grove for deeper dives. The Everglades lie just across Florida Bay.

Marathon has Sombrero Reef in the national marine sanctuary, but fishing is its main pursuit: bonefish and tarpon on the flats, sailfish offshore. It also has Key deer on Big Pine Key and cycling on the Overseas Heritage Trail. It makes a good all-round base for time on the water, but it is not a diving destination on Key Largo's level.

The two islands look in opposite directions. Key Largo is the gateway from the mainland, about an hour and a half from Miami's South Beach, Little Havana and museums, with Coral Castle in Homestead on the way. Key West is too far for a day trip from here and works better as an overnight stay.

Marathon sits halfway down the chain, so Key West's old town, Hemingway's house and Mallory Square make an easy day out, with Bahia Honda on the way. Islamorada is the outing in the other direction, and Miami is too far for a comfortable day trip.

Marathon has more for children within a short drive. There are guided visits at the Turtle Hospital, the dolphins and sea lions of the Dolphin Research Center on Grassy Key, and the nature trails and small children's museum at Crane Point. Sombrero Beach gives little ones calm, shallow water.

Key Largo is best for children old enough to snorkel. Glass-bottom boats over Pennekamp's reefs and the aquarium at the visitor centre are the highlights, but the tiny beaches leave little for younger ones. Neither island has theme parks, and both are easier outside the hot, stormy summer.

You need a car on both islands, since each is strung along the Overseas Highway and the buses are too infrequent to rely on. Marathon is the easier of the two once you arrive: it is more compact, and a bike path runs along much of it.

Key Largo's hotels, marinas and state park are spread over some 30km of highway with few pavements, and weekend traffic from the mainland slows everything down. Its advantage is the shorter drive from Miami, while Marathon is about two and a half hours down the road.

Shopping is no reason to choose either island. Both have dive and fishing gear, beachwear, T-shirts and a few galleries of local art. The difference is where you go for more: from Key Largo, the outlet mall in Florida City or Miami; from Marathon, Key West's old town.

Both are expensive, especially from December to April, when waterfront rooms, seafood dinners and charters all add up. Key Largo is slightly cheaper, and it has an option Marathon lacks: staying on the mainland in Homestead or Florida City and driving in each day.

In Marathon you save by renting a place and cooking for yourself, using the free beaches and parks, or coming in the cheaper but hotter summer months.

Neither island has performances worth planning a trip around. On both, a small community theatre and a singer with a guitar on a bar deck at sunset is about all there is. For concerts or opera, Key Largo can reach Miami's venues, while Marathon's nearest step up is the somewhat livelier theatre and music in Key West.

Both islands relax you through their slow pace rather than their facilities, and neither has any spa culture beyond the hotels. Key Largo's larger bay-side resorts run full spas and offer hammocks and yoga on the dock, but because the highway runs through the middle, you should pick a room away from the road.

Marathon is more informal, with massages at the larger resorts and a few small day spas. Its rhythm of tides and sunsets is the main way to unwind.