I have trained at quite a few gyms in Thailand and Chorenrit Muay Thai is definitely the best. Whether you just want to do some fitness work and learn some new skills or if you want to train up for a fight, the guys and Sri will help you out.
The trainer to student ration is really good, usually about 1-2 or 1-3, however when it is quiet you will often get one on one. Either way you will get plenty of personalised training over the two hours.
Mot Dang and Rob (the owner) are active fighters which really shows in the way they train you, with an emphasis on the things that are important in fighting, rather than just blasting away on the pads or baqs. Sri is also very helpful with anything you need to know about Phangan, as well as training the kids and girls who prefer a female trainer.
On my recent trip in November this year, three of the guys from the gym were fighting on the one card. All the rest of us made a night out of it and roared off on our hired motos to have a great night cheering our three guys on (they all won!).
Another thing is that Ko Phangan is a great place to stay for a beach holiday. Personally I avoid the Full Moon Party, but there is plenty of other stuff to do. The beaches are as good as anywhere, restaurants are great and you can pick and choose as to how busy or quiet you want your resort/bungalow to be. I take my family there each year and we all have a great time as I train, my wife dives and my daughter hangs out in the resort pool with the other kids.
See you there soon!