We are coming to Thailand next month and not sure which southern island to go to. Can someone please advise.
It depends what you are looking for, i have been to both Koh Tao (East coast) and Koh Lanta (west coast off Krabi).
I like Koh Tao as it is more 'un touched' and just stunning, we stayed at the coral resort which was lovely and at the end of the beach. We walked along the beach everynight to chose amongst the many little places serving dinner. Diving good on both if your into it, Koh Tao about 10 minutes to some dive sights plus but Koh Lanta more like 2 hours, however we did see 6 metre Manta rays!
Let me know if you need any more info