I second hockeymom's advice, as to making a list of what's important to you.....that's how I decided on Sandals Grande Ocho Rios in Jamaica as the right resort for our wedding group of 10 guests plus us in May this year.
When I first started planning, I knew that I wanted an adult-only, all-inclusive resort -- so a lot of the other major all-inclusives that allow kids were out (Riu, Dreams, etc.).....it's not that I have an issue with children, I was just really adament about wanting a grown-ups only wedding experience!
And once I narrowed it down to an adults-only resort, the first name I thought of was Sandals, which is a well-known resort that has years and years of experience in destination weddings, so I felt at ease with that decision. Finally, I had to pick which Sandals resort to have it at....initially, we decided on the St. Lucian Grande, but due to a few guest-related issues, we ended up going with Sandals Grande Ocho Rios, as it was both the biggest resort and also had the lowest room rates available to our guests -- a true win-win!
Anyway, our experience there was easy-breezy.....Vinette, the onsite wedding coordinator, was a seasoned wedding planning professional, and she was totally on her game, so our wedding day was smooth from start to finish!
So, the moral of the story: Iboth Mexico and Jamaica are beautiful, so you have to find the right fit for you and your fiance, and I'm sure it'll be lovely no matter where you decide to tie the knot!