The diving at Koh Tao is pretty good, but it's like a dive factory. Lots of people getting certified, lots of people on the boat. plus i think the viz this time of year may not be too good. good night life, pretty island, and chill too though.
i hear good things about koh chang, but again not sure about the viz, etc. if your in phuket, maybe koh lanta could be worth checking out, but i'm not sure about the season...
the diving around pattaya is not so good unless you go to the outer islands or make the trip to sattahip which is a little bit south of the city...
best diving i've had in SEA was in Sipadan, Sabah/ Malaysia
highly recommend angkor wat in cambodia. Laos could be the most chill place on earth. luang prabang is definately worth seeing, as is going up the mekong on the longtail boat.
within thailand, lots to do and see. it has all it all, including monkeys and elephants.
How are you able to travel so much for such an extended amount of time!?! I'm so envious!!!!! :)
Please post pics and let us know how it went!!! We have been thinking about a trip to Philippines, Vietnam, Cambodia and Laos in the future. Philippines,as you know, has great diving in Boracay.