Koh Lanta or Phuket?

Both islands put their beaches on the west coast, facing the sunset, and both are excellent from November to April. The difference is range. Koh Lanta's bays run from the easy shallows of Klong Dao and the long casuarina-lined Long Beach to small, jungle-backed coves in the south, and all of them stay fairly calm and uncrowded.

Phuket covers more ground: crowded Patong, broad family-friendly Kata and Karon, pretty coves like Nai Harn and Freedom Beach between headlands, and long, quiet sands at Mai Khao in the north. Both get dangerous monsoon surf from May to October. For island hopping, Lanta's boats go to Koh Kradan and Koh Ngai, and Phuket's go to the Racha and Similan islands.

Phuket eats far better. Its island cuisine, shaped by Hokkien and Peranakan tin-mining families, is at its best in Phuket Town: yellow Hokkien noodles, braised pork belly, crab curry with rice noodles at breakfast and dim sum in old shophouses. There is also a small fine-dining tier and good seafood at Rawai.

Koh Lanta's food is honest and cheap but narrow. The highlights are grilled seafood on the beach at night, roti and halal southern curries from its largely Muslim kitchens, and fish over the water in the Old Town, but menus aimed at visitors repeat themselves after a few days.

Neither island is a culture trip, but Phuket has enough for a full day. There is the pastel Sino-Portuguese grid of Phuket Town's old quarter with its mansions and shrines, Wat Chalong and the Big Buddha above Chalong Bay, and the Thalang museum on the Burmese siege of 1785.

Koh Lanta's heritage fits into a morning. The single stilted street of Chinese shophouses in Lanta Old Town, once a stop on the trade route between Penang and Phuket, and the Urak Lawoi sea-people village at Sang Ka U are worth seeing once.

This is where the two islands are furthest apart. Phuket has Bangla Road in Patong, a loud strip of neon bars and big clubs running into the small hours, plus sunset beach clubs on the west coast and live-music bars in Phuket Town's shophouses.

Koh Lanta's evenings mean a beach bar on Long Beach or Klong Dao with cushions on the sand, reggae and a fire show, and many of those close outside the dry season. Visitors who want a real party take the boat to Phi Phi.

Phuket has the stronger outdoors, mostly at sea. Kayaking through the limestone caves and lagoons of Phang Nga Bay is one of Thailand's great days out, and the Similan islands offer reef sharks, rays and clear water. On land there is the rainforest of Khao Phra Thaeo with its gibbons.

Koh Lanta is close behind for divers, with Koh Haa and the remote pinnacles of Hin Daeng and Hin Muang where mantas and whale sharks pass, and snorkelling at the Emerald Cave on Koh Mook. Ashore it has the national park at the southern tip and mangroves to paddle on the east coast. Most boats on both islands keep to the dry season.

Phuket gives more to choose from. Besides Phi Phi, Phang Nga Bay has the stilted Muslim village of Koh Panyee and the rural Koh Yao islands, and the bridge in the north opens road trips to Phang Nga town, Takua Pa and Krabi.

From Koh Lanta, outings mostly mean a boat to Phi Phi, about an hour away, or the fishing village on Koh Mook. Krabi Town and Ao Nang take about two hours with the car ferry, and in the monsoon the choice shrinks to almost nothing.

Phuket is easier to keep children busy on. The big resorts at Kata, Karon and the northern beaches have lagoon pools and kids' clubs, and there are two water parks, the aquarium at Cape Panwa and snorkelling boat trips. The busy roads and Patong's nightlife are things to plan around.

Koh Lanta's appeal is calm: Klong Dao's soft sand and shallow water, family bungalows with pools, and no party crowds. But there is nothing built for children, older ones may get bored, and serious medical care means a trip to Krabi.

Neither island is easy to get around without your own wheels, but Phuket is a little easier. Songthaew buses link Phuket Town to the main beaches, an airport bus runs along the west coast, and ride-hailing apps work, though the hilly roads are congested and scooters are risky.

Koh Lanta has no buses at all, just one road down the west coast, sidecar motorbike taxis and hired scooters. Arriving takes two to three hours by road and car ferry from Krabi airport, while Phuket's airport is on the island itself.

Phuket is the only one of the two worth shopping in. It has big malls in Patong and near Phuket Town, tailors who make suits in days, pearls from local farms, and the Sunday walking street and shophouse boutiques of the old quarter selling batik and Peranakan-style goods.

Koh Lanta has beachwear stalls on the main road, small night markets around Saladan and a few batik shops in the Old Town. It is fine for a sarong and nothing more.

Koh Lanta is the cheaper island. Simple beach bungalows, local guesthouses and market food are easy to find, and staying in the south or on the east coast saves more, though the transfers and tuk-tuk fares add up with no public transport.

Phuket is among Thailand's dearer destinations, with fixed-fare taxis, expensive beachfront dining and resort prices that rise steeply over the high season. Staying in Phuket Town or at Kata and Karon and eating locally narrows the gap.

Neither island has theatre or concerts, but Phuket at least offers an evening out: the long-running ladyboy cabaret revues in Patong, a large cultural show with dancers and elephants, Thai boxing nights and cover bands in the bars. On Koh Lanta the entertainment is fire twirling on the sand, a reggae band in high season and Muay Thai at small local rings.

Phuket has more depth. Its spas range from beach-road massage shops to resort pavilions over the sea, and it has a large retreat scene, with detox, yoga and meditation stays and Muay Thai fitness camps around Chalong. The quiet north at Mai Khao and Bang Tao and the bays around Nai Harn are the places to stay.

Koh Lanta has fewer options but is calm everywhere: massage in open-air pavilions on almost every beach, yoga around Long Beach, little traffic and early nights. Kantiang Bay is the most restful base, and you never have to plan around a Patong.