Koh Tao or Langkawi?

Both islands are built around their beaches, but the beaches are different. Koh Tao has one long strand at Sairee and then a scatter of small coves such as Aow Leuk and Tanote Bay, where you can snorkel straight from the sand. Some of these coves are reached down steep tracks.

Langkawi's bays are bigger and wider. Pantai Cenang and Pantai Tengah give easy swimming in shallow water, and Tanjung Rhu is a quieter casuarina-lined stretch facing limestone islets. The water there is less clear, so good snorkelling means a boat trip rather than a swim from shore.

Neither island is worth the journey for its food, and the two are close. The difference is in local character. Koh Tao's kitchens in Sairee and around Mae Haad cook largely for divers, with Thai curries alongside pizza and burgers, and nothing is really the island's own.

Langkawi has a little more to seek out. The pasar malam night markets move to a different village each evening, coastal seafood places sell fish and prawns by weight, and the canteens of Kuah serve roti canai for breakfast. Duty-free beer and wine are easy to find too.

Langkawi has more to see, though still not much. Mahsuri's tomb with its village of Malay houses, the mosque on the Kuah waterfront, the Laman Padi rice museum and the Galeria Perdana fill a morning.

Koh Tao has a couple of small temples and little else, and its 1930s past as a place of exile has left almost nothing to visit. On either island culture is a side outing, but on Koh Tao there is hardly any.

Koh Tao has the livelier evenings. Young divers and backpackers gather at the southern end of Sairee, with cushions on the sand, fire shows, bar crawls and themed parties that run into the early hours. There are no real clubs, though, and the rest of the island goes quiet early.

Langkawi's evenings are gentler: bean bags and fire-twirling on Pantai Cenang, cheap duty-free drinks and a mixed crowd of couples and families. Most of the island is dark well before midnight. It is a place for a sundowner rather than a late night.

Both islands are strong outdoors, but in different ways. Koh Tao's best scenery is underwater. Coral gardens ring the coast, and at dive sites such as Chumphon Pinnacle and Sail Rock you can see barracuda, trevally and sometimes a whale shark. On land, its granite boulders give bouldering and climbing.

Langkawi's strength is above the waterline. In Kilim, mangrove channels wind under limestone cliffs with sea eagles overhead, a cable car climbs through the Machinchang rainforest, and hornbills are often seen on Gunung Raya. Divers will prefer Koh Tao, while those after wildlife and scenery from a boat or trail will prefer Langkawi.

Neither island is a good base for outings, but Koh Tao does better. The ferry reaches Koh Phangan in about an hour and Koh Samui in about two, and both have towns, temples and markets. Monsoon seas can disrupt the crossings.

From Langkawi the realistic choice is Koh Lipe, across the border in Thailand, or a long ferry-and-road day to Alor Setar on the mainland. Most visitors there fill spare days with boat trips around the island's own islets instead.

Langkawi is far easier with children. Calm, shallow water at Cenang and Tengah, resorts with pools and kids' clubs, the Underwater World aquarium, the cable car and the mangrove boat trips fill several days of easy outings, and the roads are quiet.

Koh Tao works for older children who swim well and want to snorkel or take a junior dive course. Toddlers are harder work: the tracks down to the bays are steep, the roads are busy with novice scooter riders, and serious medical care is a boat ride away.

Langkawi is the easier island both to reach and to move around. It has an airport close to Pantai Cenang, good quiet roads, cheap car hire and ride-hailing apps that work well, and nothing is more than about forty minutes' drive away.

Koh Tao is smaller but harder going. Arriving means a long ferry day via Chumphon or Koh Samui. Beyond the walk from Sairee to Mae Haad, you depend on pickup-truck taxis, longtail boats or a scooter, and its steep, rutted hills are no place to learn to ride.

Langkawi at least gives shoppers a reason to look. The whole island is duty-free, and the big complexes in Kuah and along Cenang sell chocolate, alcohol, cosmetics and kitchenware, with batik and pearls at the stalls and night markets. Koh Tao has beachwear, T-shirts and dive gear and little more, so bring what you need. Neither island has fashion or crafts worth a special trip.

Both are cheap islands, but the money goes on different things. On Koh Tao the bargain is diving: courses are among the cheapest anywhere, and rooms are often cheaper booked through a dive school. Imported food and drink cost more, because everything arrives by boat.

On Langkawi, duty-free beer and wine, night-market meals and cheap car hire keep daily costs low, while the cable car and boat tours add up. Both islands also have resorts at international rates, so where you sleep decides most of the bill.

There is almost nothing on either island. Koh Tao has fire-dancing on the beach and the odd acoustic set. Langkawi adds cover bands and the Malay cultural shows some resorts put on over dinner, which is the closest either comes to a performance.

Langkawi is the better place to unwind properly. The rainforest resorts in the northwest and along Tanjung Rhu have serious spas using Malay herbal traditions, simple massage shops line Cenang, and the whole island moves at an unhurried pace.

Koh Tao keeps it simple, with Thai massage under a beach shelter, yoga above the bays and a few small retreats inland. For quiet, stay in the eastern bays or around Chalok Baan Kao, because Sairee is loud at night.