Hello! We were just at both propertied in January. 4 nights at the RC Krabi and 2 nights at the JW Bangkok.
The JW will treat you extremely well as a platinum. One of the best lounges of any Marriott property world wide. Its my favorite place in Bangkok. Convenient to BTS and just walking. We truly love staying there.
What can I say about the Ritz? A magnificent experience. The largest bed I have slept on in my life-twice the size of a king bed. You will have a butler assigned to you to care for your every need-and they do. There is a daily boat trip to the national park. Great snorkeling. The facilities and people at the Ritz are wonderful. The only thing I found lacking was food at dinner. Pricey (as expected) but not up to par as lunch and dinner were. I would recommend nearby restaurants. Your butler can help.
Let me know if you have specific questions. Happy to help.