hi,
i did my OWD and AOWD in Koh Lanta, which is just 1 hour from Phi Phi, and went for 2 vacations there, 40+ dives there. i have not been to Samui or Koh Tao yet, so cannot compare these, but heard lots of praise from many diving professionals in Lanta about Tao.
if I only considered
diving, now i would only go on liveboard, i got Mermaid recommended by a trusted friend. for land based diving, it is best to stay in Koh Lanta. The only worth place which cannot be done from Lanta is Similan, but Similan is far from anywhere anyway.
There are zillions of diving companies in Lanta. I personally prefer go with bigger, more comfy slowboats, than speedboats. I m on vacation, no need to rush. Two exceptions: 1) King cruiser wreck and shark point. 2) a speedboat trip to a huge gecko island Koh Rok (divers go diving while family members get wrecked on a fantastic beach), and on way back let the captain take u back through the channel between Lanta and land. With mangrove forests on both sides, water surface as mirror and boat gliding on it, great. Octopus Divers has a good speedboat and the Thai guy there, Kee, deserves his nickname "Plah", means "Fish". Now Nitrox is available, they all get it from one reliable coz German-couple-operated "gas station", membrane-stuff, the only thing they were reluctant to go over 32% to fill just 4 tanks of mine.
from
holiday point of view: in my private opinion, Phuket is only worth its airport now, this island got hit by mass tourism and sucks for anybody capable of more than just moving from hotel buffet to a (overpriced) beach chair to a topless bar. But i havnet been to all beaches and all places there. From Phuket u can take boat to PhiPhi (3-4 hours). Last time i flew to Krabi directly, went to Ralay and Ao Nang ("007: Man with golden bullet." ;-) for a trip. Phi Phi is SO beautiful, but also so famous - groups of well healed korean mothers applying their skin-whitening creams (so why do they go to tropics for holiday if they want to stay as white as on dead-bed??) and russians applying their vodkas is not my choice when it comes to neighbors on beach. But it is definitely worth to stay for 2-3 days, see it all, do sea kayak trip etc.
Lanta is good if u hv some precious halves with you who are not as obsessed with diving as you are. Very laid-back place, also during it's conservative muslim chieftain. Thousands of europeans living here long term and running dive shops, beach bars and restaurants. Also great shopping from faked stuff and local art all way to GREAT deals on diving gear. Rent a moped and explore all island...
My favourite book is Thailand: Island and beaches from Lonely Planet.
Have great holiday! Lucas