Chaloklum Diving
Chaloklum Diving is planted right in the middle of Chaloklum, the old fishing village on the north coast, and it's grown from a small operation into a proper dive center with its own facilities right there in the village β which tells you something about how long it's been going and how many people keep coming back.
What people who've dived with them tend to mention is the personal, small-group approach β this isn't a factory-line certification mill pushing groups of twenty through a pool session. Courses run from a first Open Water certification up through Divemaster, and they run trips out to Sail Rock (one of the Gulf of Thailand's best dive sites, famous for its chimney swim-through and the chance of whale sharks) as well as Ang Thong Marine Park.
Being based in Chaloklum itself means an easy walk from the village's cafes and restaurants after a dive day, rather than needing a ride back from somewhere more remote.