Phuket for beaches without a doubt and krabi - what price range for hotels ?
chaing mai try the central dungtawan hotel very nice and well located - can get to your OWN beach in Krabi / Phuket by hiring long tail boat where they will take you to seculded beach / cove with no other access other than by boat - or they also have spectacular populated beaches - avoid surin beach in Phuket too dangerous for swimming although have stayed in surin and its great again depending on price range the twin palms is out of this world and if you e mail me can point to sites with free nights etc etc