The St. Regis in Puerto Rico is beautiful - it definitely might be worth a shot. It is very close to a really nice rainforest reserve and a relatively short ride from San Juan, which has amazingly beautiful forts and colonial architecture.

I prefer the large grounds and tranquility that come with being a ways outside the city, which is why I like the St. Regis so much. But if you want to be closer to the action, the La Concha in San Juan is also a good option. I'd recommend that hotel over the Ritz Carlton in San Juan, but that also might be an option.

The Ritz Carlton Reserve in Dorado is also truly spectacular (arguably my favorite hotel in the world), but doesn't accept Bonvoy bookings as far as I know.

I also went to the Marriott in Curaçao. It was also very nice, but not as grand as the St. Regis (but this was before the renovation, so things might have changed). Curaçao also has a really neat history and interesting architecture.