I went to coki beach just a couple of weeks ago, I would go to Saphire beach if someone asked me. I wasn't that impressed with the ammenities at coki beach. People who had gone to saphire beach said it was beautiful and had alot of ammenities. It is actually connected to a hotel so you can use all the hotel during your stay. I also heard that the snorkling was much better there than at coki beach, that you didn't have to pay for chairs and it was very clean.
From what I saw it WAS much prettier.