Personally, I would stay at the Marriott. I stayed there last spring and it was very nice. It went through a $60M renovation after the last hurricane. It sits right on the edge of Charlotte Amalia and has a water taxi to downtown.
The Renaissance is nice and might be better if you have young children. The water is much calmer and all rooms have ocean views. The Renaissance and Ritz are also farther away from downtown.
I walked through the Ritz, but have not stayed their. Beautiful marble throughout and very nice, but not worth an extra 100,000 points. If you have 200,000 points, redeem them for the 7 nights plus airfare. Even if you can't use the miles with this trip, you can bank them for your next vacation.
Definitely go to St. Johns and/or take a day trip to the British Virgin Islands (Virgin Gorda, etc.)