On my third trip to Thailand I had the privilege to visit Krabi, also known as the less known neighbor of Phuket, however that is not apparent on the amount of visitors.
We actually stayed at a smaller place called Railay Beach, which is reachable by boat only. It does have it charms, less busy, especially during off-weekend days and at night. It has its own little shopping street with a bunch of restaurants and a fair number of souvenir shops and massage places.
There is East Railay Beach, with somewhat cheaper hotels and West Railay Beach that provides stunning sunsets. The better hotels are on the west side. In the direct vicinity is Ao Nang. It being on the mainland, it is more touristy and busy.