St Barts or Saint-Martin?

For beaches the two are broadly level, and both have a warm, clear sea. What differs is the kind of beach. St Barts has small, uncrowded coves, from wild, shadeless Saline and Gouverneur to Colombier, which you can reach only on foot or by boat, plus the lagoons at Grand Cul-de-Sac and St Jean with its planes overhead.

Saint-Martin has more choice in its long, busy stretches. Orient Bay is a long beach with sunbeds, water sports and a clothing-optional end. The calm west-coast bays such as Baie Rouge and Baie Longue are good for snorkelling straight off the sand. Seaweed can drift onto its Atlantic side in some months, so you may sometimes need to switch coasts.

Both islands eat in French first, with good bakeries and well-stocked supermarkets. On St Barts, though, the scene is small and nearly all at one expensive, polished level: long rosé lunches on the sand at St Jean or Saline, and terrace dinners above the harbour, with no street food.

Saint-Martin has more range and a stronger Caribbean side. Grand Case puts French and creole dining rooms over the water next to the lolos, where ribs, lobster and johnnycakes are grilled for shared tables. Conch and saltfish turn up across the island.

Neither island is a place for sightseeing, and each takes a morning at most. St Barts has its century of Swedish rule, seen in Gustavia's clock tower and the Wall House museum, and the old ways of Corossol. Saint-Martin has Fort Louis above Marigot, streets of painted creole houses and a small museum of its Arawak and salt-pan past.

On St Barts the night out is on the island itself, built around a fashionable crowd. Beach lunches at St Jean turn into afternoon parties, then the evening moves to the Gustavia harbour bars, a couple of late clubs and visiting yachts. New Year week is the loudest of all. It is strictly seasonal, though, and many places close in late summer and autumn.

The French side of Saint-Martin is calmer: dinner, then music on the street in Grand Case or sunset drinks at Orient Bay. Anyone after a late night crosses to Simpson Bay and Maho on the Dutch side for casinos and clubs. That gives more variety, but none of St Barts' glamour.

For the outdoors the two are close, and the difference is in the land. St Barts is dry, steep scrub, with the cliff path to Colombier and a few short trails to viewpoints. Saint-Martin's interior is greener and higher, with forested trails up Pic Paradis and a zipline park on its slopes.

On the water they are well matched. St Barts has turtles in its marine reserve and kitesurfing on the Grand Cul-de-Sac lagoon. Saint-Martin has reef snorkelling at Creole Rock and Tintamarre, and trade winds for kitesurfing at Orient Bay.

From St Barts there is realistically one outing: the ferry of about an hour to St Martin, for Marigot, Grand Case and Philipsburg. The nearer islands need a charter boat or a small plane.

Saint-Martin is the better base for exploring. Anguilla's long, quiet beaches are a short ferry ride from Marigot, St Barts makes a day of polished contrast, and Saba and Sint Eustatius suit one long excursion. Philipsburg and Maho Beach are a half-day out without leaving the island.

Saint-Martin suits families somewhat better. Le Galion's reef-sheltered bay and the boat hop to Pinel give small children calm water. Older children have the treetop zipline park, glass-bottom boat trips and the planes at Maho to look forward to.

St Barts is very safe and its distances are tiny. The lagoons at Grand and Petit Cul-de-Sac and Shell Beach are gentle for toddlers, and a villa pool fills much of the day. Beyond snorkelling and paddleboarding, though, older children have little to do on an island geared to couples.

On both islands you will want a hire car, but St Barts is easier because it is so small. Any beach is a short drive away and Gustavia is easy to walk, although the steep hairpin roads unsettle some drivers. Getting there is the hard part: a small plane onto a short airstrip, or the ferry.

Saint-Martin's distances run up to about forty minutes' drive. Traffic builds around Marigot, the lagoon bridges and the Dutch-side causeway, and the minibuses link only the towns. Water taxis cover the hops to Pinel and Tintamarre.

St Barts is the island for shopping. Because it is duty-free, the streets around the Gustavia harbour pack in luxury fashion, watch and jewellery boutiques to an extent few small islands match, and St Jean adds resort wear.

Saint-Martin is more modest but more varied. The waterfront market in Marigot sells spices, rum and fabrics, and Philipsburg's Front Street is lined with duty-free electronics and liquor shops for cruise passengers. Guavaberry liqueur is the souvenir with the most local character.

Neither island is cheap, but St Barts is in a class of its own for cost. Villas, beach lunches, the small-plane flight in and the car all come at prices for the very wealthy. Cooking in a villa saves a little and nothing more.

Saint-Martin is expensive too, but it leaves you some room. The lolos and supermarket picnics keep meals down, and rates drop noticeably in late spring and summer.

Neither island has a theatre or a year-round concert programme, and they differ only in what fills the gap. St Barts has a long-established January music festival, with classical music, opera and dance in Gustavia's churches. Saint-Martin's music is steel pan, zouk and soca at Grand Case and the beach bars, with calypso and soca competitions at carnival.

St Barts is the more restful of the two. Its luxury hotel spas are of a high standard, massage and yoga come to the villa, and without high-rises, casinos or crowds the island is very quiet, especially in spring. New Year week is the exception.

Saint-Martin has resort spas, independent studios and beachside yoga. You can switch off in a villa above Anse Marcel or a west-coast cove, but traffic and cruise-day crowds around Marigot are never far away.