If you traveling from Hong Kong the only direct flight is Bangkok Airlines, a god airline but no rebate.
Phuket offer direct flights on TG , KA and Thai Air Asia.
My favorites in Phuket is Sala, Six Senses in Pang Nga bay and Amanpouri.
Koh Samui have had huge development the last couple of years and is just as overdeveloped as Phuket.