Depending what you like to see and how long you plan to go on a cruise.
A cruise is always a circle, so it doesn't really matter if the cruise does stop in Mexico or everywhere else.
If you like to go to Mexico after the cruise, it's probably more depending what kind of flight you'll find...
I know only two cruise companies so far which is Costa (italian) and Royal Caribbean (USA).
For you I recommend Royal Caribbean.
Cruising from Florida there are normally two option; either cruising east with Bermudas, Bahamas etc
or cruising south with the coast of South America, Cayman Island, Jamaica involved.
In my eyes the better option is flying to San Juan in Puerto Rico as you will have only one sea day each week and every week you will visit at least 5 Islands in the lesser antilles. Search for example the "Jewel of the Seas".
But the better forum for question about cruising is "CruiseCritics.com" as there are the experts. Here in Thorntree most people will rather swim then go on a cruise (not me).