Koh Samui or Langkawi?

Both islands are built around their beaches, but Samui's are better for swimming. Chaweng's broad curve of fine white sand and clear water, the sheltered bay at Choeng Mon and boulder coves such as Silver Beach give you more choice and better water than Langkawi has.

Langkawi's Pantai Cenang is wide and shallow, with sunsets over the outer islands, and Tanjung Rhu is a lovely quiet stretch. Still, the water is pleasant rather than clear, jellyfish turn up at times, and snorkellers need a boat out to the marine park islands.

Samui eats better, largely because southern Thai cooking has more punch: fiery curries, coconut soups and grilled squid at the night markets of Lamai, Maenam and Fisherman's Village. It also has a layer of polished waterfront restaurants in Bophut.

Langkawi's travelling pasar malam, roti canai breakfasts in Kuah and seafood chosen by weight are good value but rarely memorable, and Pantai Cenang relies on ordinary tourist menus. Its duty-free status does make a beer or wine with dinner easy, unlike on the Malaysian mainland.

Neither island is a place to go for heritage, and on either one the sights fill a morning or a half-day. The difference is in flavour. Samui's are Buddhist: the Big Buddha on its causeway islet, the many-armed Guanyin at Wat Plai Laem, the mummified monk at Wat Khunaram, plus the old Chinese shophouses of Bophut. Langkawi's are Malay and rooted in legend: Mahsuri's tomb among traditional houses, the eagle statue and waterfront mosque in Kuah, and the rice-growing story at Laman Padi.

This is where the two islands differ most. Chaweng has beach clubs with DJs, open-fronted bars and clubs in the lanes behind the sand that go well past midnight, Lamai adds a rougher scene, and the full moon parties on Koh Phangan are close by. Much of it is generic, though, and parts are seedy.

On Langkawi, a night out means a beanbag on the sand at Pantai Cenang, a fire show and a cheap duty-free drink. There are no clubs of note, and most of the island is quiet well before midnight.

Langkawi has the richer landscape on the island itself. As a UNESCO Global Geopark, it offers mangrove channels and bat caves at Kilim with sea eagles overhead, ancient rainforest on the Machinchang range reached by cable car and sky bridge, the Seven Wells waterfall, and hornbills and langurs on Gunung Raya.

Samui's interior is gentler: coconut plantations, the Na Muang waterfalls and a few rough tracks. Its real strength lies offshore, in the limestone islands and emerald lake of Ang Thong and in the Sail Rock and Koh Tao dive sites, which are a serious draw for divers.

Neither island is a base for sightseeing trips, but Samui at least has neighbours worth a day. Koh Phangan, with its quieter beaches and port at Thong Sala, is under an hour away, and Koh Tao with the Koh Nang Yuan sandbar makes a full outing. From Langkawi, the only real option is Koh Lipe, which means crossing into Thailand, or a long mainland day to Alor Setar, so most visitors stick to boat tours around their own archipelago.

Both islands suit a resort-based family stay with pools and kids' clubs, and on both the attractions run out within a few days. The difference is how much care the base needs.

Langkawi feels calmer and safer throughout, with shallow water at Cenang, an aquarium, the cable car and eagle-feeding boat trips through the mangroves. On Samui, families do best at Choeng Mon, Bophut or Maenam, away from Chaweng's traffic and bars, and the busy ring road makes scooters a poor idea with children.

Samui is the harder of the two to get around. Its 51km ring road keeps distances short, but the road is busy, taxis negotiate their fares instead of using the meter and the shared songthaews keep no timetable. Scooter accidents on the hills and wet roads are common, and walking works only within each beach area, not between them.

Langkawi has no public transport either, but driving there is easy. The roads are good and lightly used, ride-hailing works well and nothing is more than about forty minutes away. The airport sits right by Pantai Cenang, the one strip you can manage on foot.

Samui is the island for browsing. You have the Friday walking street in Fisherman's Village, weekly markets in Lamai and Maenam, tailors making suits and a large mall in Chaweng. On Langkawi, shopping means stocking up: the whole island is tax-free, and the big complexes in Kuah and Cenang sell chocolate, alcohol, cosmetics and kitchenware, with batik sarongs and pearl stalls on the side.

Langkawi is the cheaper island for most trips. Mid-range hotels and chalets around Pantai Cenang, car hire, fuel and duty-free beer and wine all cost little, and only the luxury rainforest and beach resorts charge international rates.

Samui is one of the dearer places to stay in Thailand, with pricey resorts, expensive taxis, costly strip restaurants and limited flights in. Guesthouses, night-market food and massages stay cheap, though, and the north and west coasts help a careful traveller narrow the gap.

Samui gives you a few more shows to watch after dark: Muay Thai fight nights at small stadiums around Chaweng and Lamai, ladyboy cabaret and fire dancers on the beach. Langkawi has only fire-dancing on Cenang beach, cover bands in a few bars and the odd Malay cultural show over dinner at a resort. Neither island has theatre, concerts or a live-music scene worth travelling for.

Samui is the stronger choice for a restorative trip. Lamai and its hills have long been known for detox and fasting programmes, yoga and meditation retreats are spread across the island, and around Maenam and Lipa Noi the pace is genuinely slow. Just avoid noisy Chaweng.

Langkawi relaxes you through its setting rather than through programmes: light traffic, early evenings, rainforest spas in the northwest and at Tanjung Rhu that use Malay herbal traditions, and cheap massage in Cenang. Its small hot spring near Kuah is a curiosity, not a reason to go.