We stayed at the Westin Regina 3 years ago and were very pleased. Breakfast and evening hors d'ouevres on the balcony at the Royal Beach Club was very enjoyable. We've stayed at many other Cancun hotels since and except for the Ritz Carlton, thought the Westin was superior.
The only negative is that it is a longer bus ride into town, as it is located at the far end of the hotel zone.