Koh Tao or Phuket?

Koh Tao's beaches are good but small: Sairee is the one long strand, and the rest are coves such as Aow Leuk, Tanote Bay and Freedom Beach, some reached down steep tracks, with the bonus of snorkelling straight off the sand and the sandbar at Koh Nang Yuan.

Phuket simply has more beach, and more kinds of it. The west coast runs from busy Patong through broad Kata and Karon to pretty Nai Harn and the long, quiet sands of Mai Khao and Bang Tao, with boat trips to the Phi Phi and Similan islands besides. The catch is the monsoon surf from May to October, when swimming there needs real care.

On Koh Tao meals are easy refuelling: Thai curries and stir-fries, diver breakfasts, pizza and burgers around Sairee and Mae Haad, with nothing that belongs to the island itself.

Phuket has a cuisine of its own, shaped by Hokkien and Peranakan settlers, and Phuket Town is where to find it, from yellow Hokkien noodles and braised pork belly to breakfast crab curry and early-morning dim sum in shophouses. Add seafood at Rawai, evening markets and a small fine-dining tier, and food becomes a reason to leave the beach.

Koh Tao offers next to nothing here beyond a couple of small temples. Phuket at least gives a good half day or two: the Sino-Portuguese shophouses and mansions of Phuket Town's old quarter, Wat Chalong, the Big Buddha above Chalong Bay and the Thalang National Museum on the 1785 Burmese siege. Neither is a cultural destination, but only Phuket has anything to fill a rainy afternoon.

Koh Tao's evenings happen at the southern end of Sairee Beach: cushions on the sand, fire-dancers, bar crawls and a young crowd of divers and backpackers. There are no proper clubs, and the rest of the island is quiet by late evening.

Phuket goes much further. Bangla Road in Patong is a loud strip of bars and large clubs running into the small hours, seedy at the edges, while west-coast beach clubs host sunset sessions and Phuket Town has cocktail and live-music bars in old shophouses for a calmer night.

Koh Tao and Phuket are close here, and both look to the sea. Koh Tao's strength is diving on the doorstep: coral gardens around the coast, Chumphon Pinnacle and Sail Rock for barracuda and the odd whale shark, and calm sites ideal for beginners. On land it has granite boulders for climbing.

Phuket edges ahead on range. Sea kayaking among the limestone towers and caves of Phang Nga Bay has no equal on Koh Tao, the Similan islands offer top-class diving from October to May, and Khao Phra Thaeo keeps a patch of rainforest with waterfalls and gibbons.

From Koh Tao the options are few: a hop to Koh Nang Yuan, or a ferry to Koh Phangan or Koh Samui, with monsoon seas and timetables limiting how freely you move. Most people never leave.

Phuket has a broader choice by boat and road. The Phi Phi islands, the stilt village of Koh Panyee and the rural Koh Yao islands are all reachable in a day, and the bridge north opens the way to Phang Nga, Takua Pa and Krabi.

Koh Tao works only for families with older children who swim and snorkel, perhaps on a children's dive course; toddlers struggle with the steep tracks and busy scooter roads, and serious medical care means a boat ride.

Phuket is far better set up. The big resorts at Kata, Karon and the northern beaches have kids' clubs and lagoon pools, and there are water parks, the aquarium at Cape Panwa, elephant sanctuaries and gentle dry-season bays. Keep children away from Patong and from the west-coast surf in the monsoon months.

Both islands are awkward to move around and both lean on scooters, which are risky for beginners. On Koh Tao the walk from Sairee to Mae Haad pier is easy, but the east-coast bays mean pickup taxis or longtail boats over steep, rutted tracks, and getting there at all is a long ferry day.

Phuket is bigger, with an airport and a bridge to the mainland, songthaews from Phuket Town to the beaches and ride-hailing apps, but the buses do not link the beaches, taxis are costly and the coast roads clog in high season.

On Koh Tao shopping stops at beachwear, sarongs and dive gear, so bring what you need. Phuket offers a good deal more: malls in Patong and near Phuket Town, tailors who make suits in a few days, the Sunday walking street in the old quarter, and shophouse boutiques selling batik, Peranakan-style goods and local pearls.

Both are good value by Western standards, with Koh Tao a little cheaper. Its simple bungalows, Thai meals and beer cost little, and its dive courses are some of the best-value training anywhere, though anything imported by boat costs more.

Phuket is among Thailand's pricier places. Fixed-fare taxis, Patong, beachfront dining and the high season from December to March all add up, although staying in Phuket Town or at Kata and Karon and eating locally keeps costs sensible.

Neither island has a theatre or concert life, but Phuket at least fills an evening: ladyboy cabaret revues in Patong, Thai boxing nights, a large cultural theme-park show and cover bands in the bars. On Koh Tao, live entertainment amounts to fire-dancing on Sairee Beach and the occasional acoustic set.

Koh Tao's restful side is simple: a massage under a beach shelter, a yoga class above the bays and slow days in the eastern coves or around Chalok Baan Kao, away from Sairee's late nights.

Phuket makes wellness a reason to come. Massage of high quality is available at every level, from beach-road shopfronts to open-air resort spas over the sea, and there are detox, yoga and meditation retreats as well as Muay Thai and fitness camps around Chalong. Its quietest bases are Mai Khao, Nai Yang, Bang Tao and Nai Harn.