I have been to many of the Hyatt Ziva's around the world, loved all of them. Cancun was probably my favorite but Puerto Vallarta was great too as was Jamaica (great food, top shelf liquor, etc). Cancun has a new all adult tower with your own butler service. But I've been to other resorts like Sandals and Dreams always great as well.
Agree with Knights above though look at tripadvisor once you know the area you want to go to and align your budget accordingly.