Thailand's second-largest island, with almost everything on one steep west-coast road. Where you sleep decides how much of that road you drive.
Find a room before you go.
Koh Chang is mostly jungle-covered mountain. The interior is a national park with waterfalls and no roads through it, so life happens on a narrow coastal strip, and the one road that serves it climbs and drops steeply between each bay.

That has two consequences. First, the beaches feel further apart than the map suggests. Second, the hills are genuinely steep — steep enough that hired scooters are a real cause of injury here. If you are not confident on two wheels, pick a beach you can live on and use the shared songthaews instead.
Affiliate link. If you book through it we earn a commission, at no extra cost to you.
White Sand Beach (Hat Sai Khao) is the first bay after the pier and the busiest: the longest strip of hotels, bars and restaurants, and the shortest transfer from the ferry. It is convenient and social, and it is not where you go for quiet.
Klong Prao is the wide middle bay, with resorts spread thinly along a long beach and a river mouth to kayak up. It suits couples and families who want space. Kai Bae, just south, is the mid-range compromise: smaller, cheaper, with little islands offshore that make the sunsets.

Lonely Beach (Hat Tha Nam) is the young, cheap, late-night end of the island — hostels, beach bars and music, with a swimming beach that has a strong shore break. If you are here to meet people, this is the address. If you are here to sleep, it is not.
Bang Bao at the southern end is not a beach at all but a fishing village built along a wooden pier over the water, now lined with seafood restaurants and dive shops. Most boat trips to the outer islands leave from here. Beyond it, the far south-east has remote bays reached by rough road — beautiful, and a long way from everything.

Klong Prao or Kai Bae. Both have swimming, restaurants within reach and a calmer feel than White Sand Beach, without being isolated.
Yes, particularly Klong Prao, which has space, long sand and resorts built for it. Lonely Beach is the one to avoid.
It helps, but the hills are steep and accidents are common. Shared songthaews cover the west coast road and are a sensible alternative.
By bus or minivan to Trat, then a car ferry from one of the mainland piers. The crossing takes around thirty minutes.
More Koh Chang and eastern Gulf guides, plus the rest of Thailand's islands.