If you live in the cayes, AC?, you're in for a lot of maintenance.
I brought a 21 speed Mongoose down, bought used in Miami.
Within 6 months all the cables and de-railers were rusted solid from the salt air.
it is now a 1 speed, and it's all you need here, so I leave it that way.
The suspension on a mountain bike is very stiff, doesn't make it more comfortable to ride either.
I've had both here, would not buy another mountain bike for the cayes.