Miami Beach or St. Pete Beach?

These are two very good beaches, but on different seas. Miami Beach has about 11km of wide sand on the Atlantic, and the water is warm enough for swimming even in winter. Each stretch has its own mood, from South Beach, with its crowds and people-watching, to the calmer sand at North Beach, and a beachwalk runs behind the dunes.

St. Pete Beach faces west onto the Gulf, where the water is shallower and stiller and the evening ends with the sun setting over the sea. Pass-a-Grille has low buildings and plenty of room, and Fort De Soto and Shell Key add beaches with almost nothing built on them. The trade-off is a cool sea in winter and the occasional spell of red tide.

Miami Beach eats better and with more variety. Cuban sandwiches, croquetas and strong cafecito from takeaway windows sit alongside chef-led dining rooms, ceviche, arepas and winter stone crabs. The tourist menus on Ocean Drive are best skipped, and Little Havana is just across the causeway.

St. Pete Beach keeps it simple, with grouper sandwiches, fried shrimp and smoked fish spread eaten on a deck at sunset. That is pleasant for a few nights, but the choice soon narrows to chains along Gulf Boulevard, and the more ambitious cooking is a drive away in St. Petersburg.

Miami Beach has a real sight of its own: hundreds of 1930s Art Deco hotels in pastel stucco, best seen on foot along Ocean Drive and Collins Avenue. The Wolfsonian's design collection, the Bass, the Holocaust Memorial and the winter Art Basel fair add enough for a couple of days.

St. Pete Beach offers a pink 1920s Mediterranean Revival hotel, the old cottages and small history museum in Pass-a-Grille, and the Spanish-American War batteries at Fort De Soto. That is a morning's sightseeing at most, so anyone who wants museums will be crossing the bay.

This is where the two differ most. South Beach is one of the best-known places in the world for a night out. There are clubs with guest DJs until dawn and afternoon pool parties, and Collins and Washington avenues stay loud into the small hours. Expect dress codes, door policies and high prices, while Sunset Harbour offers quieter cocktail bars.

In St. Pete Beach the evening peaks at sunset, with tiki decks, beach bars and a cover band. Corey Avenue has a few livelier bars, but there are no clubs, and a late night means driving to downtown St. Petersburg.

Both are flat barrier islands where outdoor life happens on the water, and they are about level. The difference is where it happens. Miami Beach's best nature is a trip out: reefs and wrecks offshore for divers and snorkellers, mangrove paddling at Oleta River, and Biscayne National Park's keys and the Everglades' sawgrass farther afield.

At St. Pete Beach the wildlife is right on your doorstep. Kayak trails wind through the mangroves at Fort De Soto and Shell Key, dolphins follow the boats, manatees arrive in the cooler months and roseate spoonbills feed on the flats. It suits birdwatchers and paddlers more than divers.

Both have a good choice of day trips, and almost all of them need a car. From Miami Beach the best are on the mainland: Little Havana, the Wynwood murals, Vizcaya's villa and gardens and Coral Gables. Beyond that, Palm Beach's mansions and Key Largo, the first of the Florida Keys, are within reach.

St. Pete Beach has more variety within an hour. There is the Dalí Museum in St. Petersburg, the cigar-factory streets of Ybor City in Tampa, the Greek sponge docks of Tarpon Springs and the Ringling estate in Sarasota. Orlando's theme parks are possible on a long day.

St. Pete Beach is the easier choice with small children. The Gulf is shallow and usually calm, and the hotels on Gulf Boulevard often open straight onto the sand. Shelling at Shell Key, dolphin boats and the fishing pier at Fort De Soto fill the days, and there are aquariums in Clearwater and Tampa.

Miami Beach can work well too, with lifeguards along the whole shore and quieter resort pools in Mid-Beach and towards Surfside. However, South Beach is a party district, especially at weekends and during spring break, and the zoo and science museum are on the mainland.

You can manage Miami Beach without a car for much longer. South Beach is flat and compact, with the beach, the Art Deco streets and Lincoln Road a short walk apart, and free trolleys and buses run up Collins Avenue. Leaving the island is the weak point, because there is no rail link and the causeways jam.

St. Pete Beach is one long strip with a beach trolley and two small walkable centres. Fort De Soto, St. Petersburg and Tampa's airport all mean driving, so most visitors hire a car from the start.

For a serious shopping trip, Miami Beach is well ahead. That is mostly thanks to Bal Harbour, at the northern tip of the island, where the big European fashion and jewellery houses share one open-air mall that draws wealthy shoppers from across Latin America. Lincoln Road works better as a palm-lined walk after dinner than as a place to find anything unusual, and Collins Avenue covers swimwear and resort clothes.

St. Pete Beach has the shops you would expect in a small beach town, with sun hats, beach gear and souvenirs along Gulf Boulevard. Its handful of independent boutiques, galleries and craft shops on Corey Avenue and in Pass-a-Grille have more local character than the chain stores on Lincoln Road, but they won't fill more than an hour. For anything bigger you have to drive inland to St. Petersburg or Tampa.

Both are expensive American beach towns, but Miami Beach costs more. Resort fees, parking charges, service charges and South Beach cocktail and club prices all add to the bill, and winter is the most expensive season. Staying on the side streets or in North Beach, or coming in summer, helps.

St. Pete Beach is easier to keep within a budget, with older motels a block back from the sand and casual seafood places. A hire car eats into the saving, and rates peak from February to April, when visitors from the north arrive.

Miami Beach has more going on than its party reputation suggests. The New World Symphony plays in Frank Gehry's hall on 17th Street, with some concerts projected onto the outside wall for people sitting on the lawn. Miami City Ballet is based on the island, and the Jackie Gleason and Colony theatres host touring shows and smaller productions from autumn to spring.

St. Pete Beach's live music is cover bands and acoustic sets in beach bars. For the Florida Orchestra or a touring musical, you have to drive to St. Petersburg or Tampa.

Miami Beach has more to offer in spa facilities. Several large resort spas have hydrotherapy circuits with saunas, steam rooms and plunge pools, and sunrise yoga on the sand is a regular sight. For a restful week, stay in Mid-Beach or towards Surfside rather than in loud South Beach.

St. Pete Beach has fewer spas, mostly in the bigger resorts and a few day spas along Gulf Boulevard. What it does offer is a slow pace without much effort, with morning walks on the sand, long afternoons and an unhurried feel in Pass-a-Grille outside spring break.