A long island with one road, nine beaches and none of the noise the Andaman coast is famous for.
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Koh Lanta is thirty kilometres long and has essentially one road down the west side, with beaches strung along it like beads. Klong Dao at the north end is the family beach, shallow and calm. Long Beach is the backpacker middle. Further south — Klong Nin, Kantiang, Bakantiang — the bays get smaller, prettier and quieter, and the road gets worse.

On the east coast, Lanta Old Town is the island's other side: Chinese-Thai shophouses on stilts over the water, sea gypsy villages, and seafood restaurants on the piers. Nothing happens fast here, which is exactly the point.
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Most people come through Krabi. Minivans run from Krabi town and the airport in about two hours, crossing on the car ferries at the north end — or over the bridge, depending on which route your driver takes.
From the Gulf side, cross the peninsula: bus or train to Surat Thani, then a minivan to Krabi and on to Lanta. It is a full day but a straightforward one, and 12go sells the whole chain as one ticket.
In high season, speedboats connect Lanta with Phi Phi, Koh Jum and Railay, which makes island hopping easy. Those boats stop running in the monsoon.

North for convenience, south for beauty. Klong Dao and Long Beach put you close to the ferry, the shops and the widest choice of restaurants; Klong Nin is the sweet spot in the middle; Kantiang and beyond are for people happy to ride twenty minutes for dinner.