IMHO the Sheraton Retiro has the best outdoor pool, almost 50 mts, tennis courts , full size gym, SPA/Sauna massage, full bar and food service at the pool side. Has a day pass system which allows you to use all the facilities. Can`t beat that.
The Four Seasons pool is gorgeous. It used to be you could use it all day if you did a spa treatment. Not sure if it's still the case...it has been ages. Here's a pic.