I recently went and I think my favorite island was Koh Lanta. It is not super commercialized like Phuket and still absolutely beautiful. We rented a scooter and

I recently went and I think my favorite island was Koh Lanta. It is not super commercialized like Phuket and still absolutely beautiful. We rented a scooter and cruised around the whole island where we could pull up to any beach we wanted on our own time. Most of the southern beaches had maybe 1 or 2 people. There is also a really cool national park at the southern tip. I would also recommend taking a day trip to Koh Phi Phi/Maya bay, however go very very early. It will get crowded quickly, but it is one of the most amazing places I've ever been too. I have never seen water that blue in my entire life. Highly recommend going snorkling there if you get a chance. Another semi low-key spot we went to was Railay Beach/Ao Nang. It wasn't low-key as Koh Lanta but it was a lot of fun and not very commercialized. We actually completely stayed away from Phuket other than flying into the airport. The above suggestions were all from some friends that lived there for a couple years and we had an absolute blast.