St Croix or Vieques?

Both islands are built around the beach, with water warm enough to swim in all year. They differ in style. St Croix offers long, quiet western sands at Sandy Point and Rainbow Beach, snorkelling from the shore at Cane Bay, small reef-sheltered coves near Christiansted and the white beach on Buck Island.

Vieques has more beaches, and they are emptier. They run from the shaded crescent of Sun Bay to the reef-fringed coves of Caracas, Pata Prieta and La Chiva inside the refuge. The cost is comfort, because there are no lifeguards, cafés or sunbeds, and you often reach the sand along a bumpy track.

St Croix gives you more to eat. Crucian dishes such as kallaloo, goat stew with fungi, johnny cakes and Indo-Caribbean roti come from roadside stands, and Christiansted's old streets have a real cluster of restaurants with a small fine-dining tier. Visiting the rum distilleries near Frederiksted adds an outing.

Vieques eats Puerto Rican: mofongo and grilled fish on Esperanza's seafront, alcapurrias from kiosks, bakeries in Isabel Segunda. The choice is smaller, and kitchens may close for days out of season, so self-caterers are better off shopping on the main island first.

On sightseeing St Croix is well ahead. Christiansted's ochre arcades, the Steeple Building and Fort Christiansvaern make up a preserved colonial waterfront. Frederiksted's red fort, where emancipation was proclaimed in 1848, the Whim estate and the hilltop sugar-mill ruins trace the island's history of slavery and sugar.

Vieques has the small Fortín Conde de Mirasol and its museum, a pair of lighthouses and an ancient ceiba tree. Its most compelling story is the decades it spent as a naval bombing range, and you can take it all in during an afternoon.

Neither island stays up late, but St Croix at least gives you somewhere to go. Open-air bars along the Christiansted boardwalk and in its courtyards draw sailors, locals and visitors. The Christmas festival season brings street parties that run late.

On Vieques an evening means a rum punch at one of a few seafront bars in Esperanza. For many visitors the only reason to go out after dark is the kayak trip on the bioluminescent bay.

St Croix has more variety outdoors, and most of it is underwater. There is the marked coral trail at Buck Island Reef, the wall dive at Cane Bay and the night dive off Frederiksted pier. On land it adds coastal trails to Point Udall, a patch of north-western rainforest, nesting leatherbacks at Sandy Point and a glowing bay to paddle at Salt River.

The highlight on Vieques is Mosquito Bay, one of the brightest bioluminescent lagoons anywhere, best visited away from the full moon. Beyond that you get dry-forest refuge, birding, cycling tracks, wandering horses and easy snorkelling with turtles and rays. There is nothing steep to hike.

Both islands are places to stay put. St Croix has the slightly better escape: a seaplane reaches St Thomas or the national park beaches of St John in about twenty minutes, although it makes for a full and fairly costly day.

From Vieques, the best outing is Culebra and Flamenco Beach on a chartered boat. Old San Juan means a ferry or short flight and then a drive, which makes for a long day.

Families do roughly as well on either island, and on both the days revolve around calm water, with nothing built for children. St Croix gives an easy first snorkel at Buck Island, paddling at Rainbow Beach and a fort to clamber over. Most families stay at a resort or villa with a pool.

Vieques swaps the fort for semi-wild horses by the road and a night kayak through glowing water that older children remember for years. The ferry, the jeep, beaches with no lifeguards and limited medical care all mean more planning with small children.

St Croix is the easier island to travel around. A hire car takes you from Christiansted to Frederiksted in about forty minutes, mostly on decent roads, though traffic drives on the left and the north-shore climb is steep and winding. Both towns are pleasant to walk.

On Vieques the effort starts before you land, with ferries from Ceiba that sell out or change times, or a small plane. On the island you need a jeep for the dirt roads into the refuge, and jeeps are scarce, so book well ahead. Shared públicos cover only the run between the ferry and Esperanza.

There is little to buy on either island, but St Croix has more. Christiansted's arcaded streets hold jewellers making the Crucian hook bracelet, Caribbean art galleries and shops selling local rum and hot sauce. On Vieques you will find a few galleries and craft shops in Esperanza and Isabel Segunda, and otherwise the grocery store.

Both are expensive islands where almost everything is shipped in, and a car is a necessary daily cost. On St Croix, the ways to save are local food stands and simple guesthouses in Christiansted.

On Vieques the savings come from taking the ferry rather than flying, cooking in a rented house and staying in a plain guesthouse in Esperanza. The jeep, though, is a cost you cannot avoid.

St Croix has a living folk tradition. Quelbe scratch bands and stilt-walking mocko jumbies appear at the Christmas festival and the winter agricultural fair, and there is a small performing arts centre and open-air jazz on the Frederiksted waterfront.

Vieques has almost nothing. You might hear a guitarist in an Esperanza bar, and once a year the patron saint festivities bring bomba and plena to Isabel Segunda's square.

On both islands rest comes from the slow pace rather than from treatments, and neither suits anyone looking for a proper spa. St Croix has a few resort spas, and the quiet West End or a villa in the eastern hills makes it easy to do nothing. Vieques keeps things simpler, with yoga and massage at guesthouses, no high-rises and roosters instead of traffic.