Advice on Mexico all-inclusive please? (for 2 sisters)?

My sister and I want to go to Cancun/Playa Del Carmen/Riviera Maya. We're in our late 20s. I want to relax on an awesome beach & prefer adult only, my sister wants access to nightlife. We have decided all inclusive is the way to go. Any tips for us as far as location/hotels? I really want the food to be good too! I have been the Gran Melia Cancun before but that was for my senior trip many years ago. We want to stay 8 nights & are only interested in 4+ star resorts. Thanks for your tips!