Monkey bay is a was horrible. Maya Bay was a beautiful. But do not do a tour, which takes you to monkey bay and a bunch of snorkel spots. Reason being, the snorkeling wasn't that great. Monkey bay was sad. And garbage filled. As for maya bay, they drop you off on the back side since its low season and Unless you can get there when the tide is at its highest. The waves smash you and the 3 dozen other people into the sharp rocks as your funneling your way along these ropes to a ladder. And the you only have an hour or less to enjoy the beach. If you can, rent. Long tale boat for 3,000 to 4,000bt ( Thai dollar ) and get them to take you to maya bay ( best split between 4-6 people )
Koh Phi Phi Don which is the main island. Is an over crowded party island ( give you an example around 10 dive shops in a KM radius) Beach is nothing to rave about.
Try long island or the other one that was suggested ( haven't gone to those yet ) about 7 years ago