Hi cryptojam! It's usually cheapest to fly in Bangkok but everyone I have ever talked to finds it ends it's magical allure after only a few short days.

You have 2 sides of islands to choose from basically. You can fly into Krabi one the west side, or Ko Samui on the east.

Ko Samui, a relatively small island, easy to get around on a motorbike, beaches, island-y feel
Ko Pha Ngan, where the full moon parties happen (take boat from Ko Samui)
Ko Tao, an even smaller island with a relaxed atmosphere

And the other side which is
Krabi (have not been yet)
Ko Lanta (^)
Phi Phi (gorgeous islands that you must get to by boat. Usually from Phuket but they have boats that take you from one side to the other)
Phuket: Patong if you're looking to party, Phuket Town if you want to see the culture.

Chiang Mai (North)
-gorgeous landscapes, jungles, elephants
-still city life but an easy escape into nature

I'm about to do a blog on this soon ;)

Reach out if you need anything else!
XO,
@heart-to-heart

Hope this helps a bit! :)