One of the best beaches in Thailand can be found here Phra Nang. Waters are clear, emerald green and tranquil. The only caveat is the number long-tails boat (known as Ruea Hang Yao). They arrive in hoards, full of tourists between 9am and midday. Thankfully the beach is long enough to find some private space.
We stayed in a resort called Rayavadee, which backed onto Phra Nang Beach, and also was fronted by Railay beach. I would say this is definetly the best resort in the area to stay for position, quality and service. However its not the cheapest price wise. You can find more budget places to stay along railay beach. The area is also home to a number of animals which include a variety of monkeys. Such as the macaques, and Dusky leaf mokeys.
In terms of things to do, of course you have the amazing beaches so you can just chill and relax. There are a number of food options along Railay beach, (non on Pha Nang unless you stay at the Rayavadee resort). Railay beach also has thai massages available. If I had to choose the “better” of the two beaches then Phra Nang Beach is nicer. Just a shame that you get so many boat loads of tourists thought thats the only downside. You do howver have the option to take a boat ride to some of the smaller islands several miles out. So that is always an option.