We do an all inclusive at least once a year and have since 1999. Hands down you will get more bang for your buck and much better service in Mexico than in Jamaica.
We did stay at the Iberostar Grand Rose Hall in Jamaica a couple of years ago. We had previously sworn off Jamaica after a couple of disappointing trips, but decided to give it another try since Iberostars get such great reviews and they had just opened a beautiful property in Jamaica. The Iberostars in the Maya Riviera in Mexico are far superior in terms of service and amenities than the one in Jamaica.
We also really enjoyed the Dominican Republic for all-inclusive but there are alot more off-site tours, excursions in Mexico if you are interested in leaving the resort. E.g. In the Mayan Riviera, you can swim in underground rivers (Cenotes), visit ancient Mayan Ruins, swim in natural salt or fresh water aquariums.
I like the laid back feel of Jamaica, but if you want to be pampered and treated like Royalty, Mexico is the way to go.