Florida Keys or Siesta Key?

This is Siesta Key's strongest card. Siesta Beach is a wide stretch of soft white quartz sand that stays cool underfoot and slopes into calm, shallow water. Crescent Beach and Turtle Beach add quieter sand, snorkelling at Point of Rocks and hunting for shark teeth.

The Keys have warmer water, especially in winter, but the reef stops the waves that build sand, so most of the shore is mangrove, rock or shallow flats with seaweed. Bahia Honda, Sombrero Beach in Marathon and Smathers Beach in Key West are the exceptions worth planning around.

The Keys give you more to seek out. Yellowtail snapper and hogfish come straight off the boat, conch fritters and spiny lobster are local staples, and Key West's Cuban heritage brings strong café con leche and Cuban sandwiches. You can also often have your own catch cooked for you.

Siesta Key eats in a simpler beach style, mostly grouper sandwiches, shrimp baskets and fish tacos on open-air decks around the village. For a proper dinner you drive to downtown Sarasota or St Armands Circle, which have the wider choice.

Neither place is a culture destination, but the Keys have their heritage on the spot. In Key West you stay among wooden conch houses and Victorian porches, with the Hemingway Home, the Truman Little White House and the brick forts, and Fort Jefferson is out in the Dry Tortugas.

Siesta Key itself has no museums or landmarks, so you go to Sarasota for culture. There the Ringling's Rubens canvases, the Ca' d'Zan mansion and the circus museum make a fine single day, alongside the Selby gardens and mid-century modern houses.

Duval Street puts the Keys far ahead. The night starts with the sunset crowd at Mallory Square and runs through open-sided bars, rooftop decks and old saloons until very late. There is also a long-established gay scene with drag cabaret at the lower end.

On Siesta Key you get a few blocks of village bars with cover bands and frozen cocktails, livelier at spring break and quiet well before the small hours. Sarasota's cocktail bars make for a calmer, more grown-up evening.

The Keys win because so much happens under and on the water. You can snorkel and dive the reef at John Pennekamp and Looe Key, explore wrecks off Key Largo, fish the bay-side flats for tarpon and permit, and see tiny Key deer in the Lower Keys. Bear in mind that much of the coral is patchy and heat-stressed.

Siesta's nature is gentler: dolphins seen from the beach, manatees in the cooler months, nesting turtles, and kayaking through the mangrove tunnels on Lido Key. Myakka River State Park adds alligators and a canopy walkway, but there is no reef to match the Keys'.

Siesta Key has the wider choice. St Petersburg's Dalí Museum is about an hour away over the Sunshine Skyway, and Tampa's Ybor City, the sponge docks of Tarpon Springs, Anna Maria Island and Venice give real variety in both directions along the Gulf.

From the Keys there are really two outings: Miami, if you stay in the Upper Keys, and the boat to the Dry Tortugas from Key West. Driving the Overseas Highway is lovely, but one island town looks much like the next.

Siesta Key is the easier place with young children. The main beach is shallow enough for toddlers to paddle far out and has lifeguards, a playground and showers, and a rented condo with a pool makes long stays simple. Mote Marine Aquarium is the main outing away from the sand.

In the Keys it works best to stay in Marathon or Islamorada, where children get the sea turtle hospital, the dolphin centres and glass-bottom boats at Pennekamp. Key West's drinking streets and the long drive down the chain make it harder work.

Both need a car once you want more than one place, but the difference lies in what you drive. In the Keys it is a single highway of about 180km over more than forty bridges, so any hold-up stops everything. Key West's flat Old Town is the place to leave the car and walk or cycle.

Siesta Key is only about 13km long, and a free trolley runs its length, so a beach-only stay works without a car. Going further means crossing two bridges that clog in winter, but Tampa and Sarasota airports are both an easy drive.

In the Keys, shopping is a stroll around Key West and not much more. Duval Street sells T-shirts, hand-rolled cigars, hot sauce and Key lime products. The side streets of Old Town are better for local painting, handmade sandals and sea-glass jewellery. Further up the chain you will find little beyond dive shops and roadside shell stalls.

Siesta Key gives you more to browse within reach. Its village sells swimwear and sandals, and the more upmarket shops are about twenty minutes away at St Armands Circle, a ring of boutiques, jewellers and resort-wear shops. Sarasota's Main Street adds galleries, bookshops and independent stores. That fills a rainy afternoon nicely, but nobody plans a trip around it.

Both are expensive, but the Keys more so. Everything comes down one road, and winter rates in Key West and Islamorada are among the steepest anywhere, with charters and dive trips adding up fast. Marathon and the Lower Keys soften the bill a little.

On Siesta Key the beach and the trolley are free, and renting a condo with a kitchen lets you control what you spend on food. Summer is cheaper in both places, but you pay for that in heat and storms.

Thanks to Sarasota, Siesta Key comes out well ahead. The city has a resident opera company in its restored 1920s opera house, the Asolo Rep at the Ringling, a ballet company, a symphony and touring shows at the Van Wezel hall, mostly from autumn to spring.

Key West has the Tennessee Williams Theatre and a short symphony season. Most of its live music is acoustic sets, cover bands and drag cabaret in the Duval Street bars.

Neither has a spa culture, and both help you relax mostly through their slow pace. In the Keys the quiet choice is a cottage on the water in the Middle or Lower Keys, or a resort spa on a private island near Islamorada. Siesta Key's version is beach yoga, morning walks and the especially quiet south end around Crescent and Turtle beaches.