'Sounds like you've had bad luck in Phi Phi'
Not really. I was close so went to see what the fuss was about. It's a small island, and basically overcrowded, so it ruins the whole experience. The water was dirty, not good for swimming, doesn't sound like paradise to me.
Just to answer the last post, I thought Ko Samui was great for my taste. I cannot compare to many islands in Thailand since I have only been to a few; I mostly do the island thing in Malaysia. The south end of Chaweng Beach in Samui is not very crowded at all. The sea is clean. There are few watercraft. The sea is usually calm for relaxing swimming, but may get rough in the case of nearby storms for body slamming waves. Conveniences, services, food, hotel, trasportation, are nearby and open late. There are nightclubs in Chaweng with good music; those are 2km from the south end of the beach, in walking distance but the Songthaew run all night. Prices are high for those south end hotels, with the exception of a few that are a few minutes walk from the beach. We stayed at Lucky Home, and we were so lucky to find it.
Locals say they prefer Ko Tao to Ko Samui; locals say there are too many tourists in Ko Samui. There may be many tourists, true, but you can get away from the majority of tourists in Ko Samui and still enjoy the loads of services and restaurants that a high amount of tourists' patronage allows.
I just got back from my trip to Phi Phi and I have to say I had a great time. The weather was a little disappointing, but it was exactly what I needed after five days at Pha-Ngan. I didn't find either place dirty, but I have a good tolerance thanks to a lot of travel experience in developing countries. I'd definitely recommend the island.