We have stayed in Royal Suites Yucatan once and Royal Suites Turquesa three times. Personally, I far prefer Royal Suites Turquesa. Firstly, yes it is as beautiful as the photos depict it. RST truly has the feel of a separate adult only hotel being separate from the rest of the resort while RSY is placed in the middle of other parts of the complex and having a beach area some distance away. The dining opportunities in RST are also different than in RSY. El Jardin is open for breakfast and dinner, while the Royal Gourmet is open for breakfast, lunch, and dinner. Add to that Le Chanterele, the French restaurant.
Both resorts offer similar quality and service. However, the physical differences between the two hotels is great.