just one more thing to consider....
if I was in your situation I would think about the work load of medical school and making sure you are able to handle it. before attending medical school I thought that modivation alone would be enough to get through medical school despite prior poor academic performance. I have now realized that it is a tremendous amount of work and it is necessary to already have excellent study skills which is normally goes with good marks. There is very little options available if you don't do well at a caribbean school.
I don't want to sound negative at all, but just want to suggest that you consider (if you already haven't) what you will do differently considering your existing makers. The premed program from what I have heard (didn't do premed but know people who have) is that is gets progressively difficult over the duration of the term and many don't make it through if they don't have good study skills and motivation.

regarding choosing between MUA and SGU. if money is not an issue I would choose SGU over MUA because of their reputation and that you have more advanced facilities available that may help you learn.