I had an absolutely incredible time with big blue. They were the one company on the island that had a dedicated boat for "fun divers," which was the original reason I went with them. I am so happy I did, what an awesome place! The location is prime, right on the beach, and I spent countless afternoons sitting at the restaurant chatting with new friends and sipping fruit juices. The diving is professional and the staff is excited and passionate about what they do. They could take a dive with crappy visibility and still find awesome things for you to look at. If you get a chance to dive with Steven, take it! He is amazing! The vibes on Koh Tao are so relaxed and if you are looking for a diving getaway, I would definitely recommend. Only negatives I can think of were that we had a really bad night dive that probably wasn't the safest, ending in a 25 minute surface swim against the current back to the boat. Of my 13 dives with big blue, I'm bummed that there was one that stuck out in my mind as a bad dive.. Also the free dorms are pretty shocking, but they are free so you can't really complain.