Thailand rules, although personally I wasn't a big fan of Pattaya.. I think I went into sensory overload or something
I loved Phuket, although from the pictures I saw of it after the tsunami, there might not be much there anymore.
If you have time, you should go check out Chiang Mai in the north as well. It isn't a beach area and is a lot more subdued than the other parts, but it's a nice town & you can get up into the mountains from there. Go see a temple & maybe check out the hill tribes.
If what you want is hookers and booze, stay in the south
