maya beach was mental busy, and always will be. check it out. there were boats parked from end to the other. and there's nothing there, no hotels or anything..
railay beach was ok, but very overcrowded. but i was there at peak season. nothing much there though. to do anything you'd have to get a longtail around to ao nang.
for chilling out by a pool helen, ao nang was great and plenty of resorts there to choose from. however, on samui you don't need a pool as the sea is so nice.