Koh Tao or Phu Quoc?

Both islands are beach trips first, but their beaches are different in kind. Koh Tao is mostly small coves, many of them down steep tracks. Sairee is its one long strand, and at bays such as Aow Leuk and Tanote you can snorkel straight off the sand.

Phu Quoc has the long beaches. Long Beach runs some 20km down the west coast, and the whitest sand and palest water are at Sao and Khem in the southeast. Their best seasons also differ: Phu Quoc's west coast is calmest in the dry months around the turn of the year, exactly when Koh Tao's east coast is hit by the monsoon.

On Phu Quoc more of what you eat belongs to the island. There is seafood picked live from tanks, raw herring salad rolled in rice paper, the evening market in Duong Dong and restaurants on stilts over the water at Ham Ninh. You can also visit the fish sauce houses and pepper farms behind its two best-known products.

On Koh Tao, meals in Sairee and Mae Haad are Thai curries and fruit shakes next to the pizza and breakfast cafés that feed the divers. The food is cheap and easy, but none of it is the island's own.

Neither island is a heritage trip, but Phu Quoc gives you at least an afternoon of it. There is the old prison near An Thoi, now a sober museum of the French and American wars, the Dinh Cau shrine in Duong Dong and the hillside Ho Quoc Pagoda. Koh Tao has a couple of small temples and almost nothing else, so sightseeing barely features there.

Koh Tao has the livelier evenings, though they happen in one place: the southern end of Sairee Beach. There are cushions on the sand and fire-dancers, plus bar crawls and music into the early hours for a young crowd of divers and backpackers.

Phu Quoc's nights are calmer and more spread out. You get sundowners on Long Beach, a few bars in Duong Dong, people strolling the lit-up entertainment districts and a casino in the north. Most visitors are back at their resort well before midnight.

If the outdoors for you means the sea, Koh Tao is the stronger choice. Coral gardens ring the coast, and dive boats reach pinnacles such as Chumphon Pinnacle and Sail Rock, where barracuda gather and whale sharks sometimes pass. The calm, warm sites suit beginners. On land there are granite boulders to climb and short, steep trails to viewpoints.

Phu Quoc's reefs off the An Thoi islands are pleasant rather than memorable. Its wilder side is the forested national park in the north, with a few trails and streams, and the cable car to Hon Thom gives the widest views of the archipelago.

On both islands most people stay put, but Koh Tao has more within reach. Koh Phangan is about an hour away by ferry and Koh Samui about two, each with towns, temples and markets, and the Koh Nang Yuan sandbar is a short hop. Rough seas in the monsoon can cut those plans short.

From Phu Quoc the options are island-hopping boats round the An Thoi archipelago, or the ferry to Ha Tien, a quiet border town with a temple hill, a little over an hour away.

Phu Quoc is far easier with children. The north has a safari park you drive through and a theme park with an aquarium, the cable car to Hon Thom ends at a water park, and the big resorts on the west and north coasts have pools and kids' clubs. These sights are spread out, so expect a taxi for every outing.

Koh Tao works for older children who swim well and might try a children's dive course. With toddlers, the steep tracks, roads full of inexperienced scooter riders and the boat ride to serious medical care all count against it.

Phu Quoc is the bigger island but the simpler one to get around. The airport sits beside Long Beach, the roads are good, electric buses run along the main road through the island, and ride-hailing apps and metered taxis cover the rest. The far corners are half an hour or more by road, so you will ride rather than walk.

Koh Tao is small but awkward. Only the stretch from Sairee to Mae Haad is easy on foot, and the roads to the east coast bays are steep and rutted, with no buses. Just reaching the island means a ferry and a long travel day.

Neither island is worth visiting for shopping. Phu Quoc offers a little more to take home: black pepper, dried seafood and cultured pearls from the island's farms, plus the Duong Dong evening market to browse. Koh Tao has little beyond sarongs, T-shirts and dive gear, so buy anything you need before you get on the ferry.

Both islands are inexpensive by world standards, but the costs fall in different places. On Koh Tao the bargain is the diving. Courses are among the cheapest anywhere, and rooms are often cheaper if you book through a dive school, but imported food and drink cost more because everything arrives by boat.

On Phu Quoc, local food, guesthouses and taxis are cheap. Most of the budget goes on the theme parks, the cable car, boat trips and the big beach resorts, especially during the dry-season peak.

Anyone who plans evenings around theatre, concerts or traditional dance will find nothing to book on Koh Tao. Performance there is informal and happens by chance, a guitarist playing in a beach bar at most, and the island has no stage of any kind.

Phu Quoc at least gives you a planned night out. The resort districts at either end of the island put on big outdoor spectacles after dark, with the one in the south played out over the sea. They are polished enough to fill an evening, though nothing in them comes from Vietnamese tradition. You will not find a concert hall, a theatre or local musicians, so treat these shows as entertainment rather than culture.

Phu Quoc suits a slow, pampered stay better. There is cheap Vietnamese massage in Duong Dong, resort spas with herbal baths, and quiet places to stay on the north coast around Ong Lang and Ganh Dau or near Khem Beach.

Koh Tao has massage under beach shelters, yoga above the bays and a few hillside spas, but relaxing there mostly means swimming and resting. Stay in the eastern bays or at Chalok Baan Kao, because Sairee is loud at night.