Saba and MUA Nevis are very close to being the same.
MUA Belize is NOT affiliated with Saba or MUA Nevis.
Saba is more established than MUA Nevis. However, Nevis is a very very close second. I attended MUA Nevis and it is a good school.
MUA Belize is having its own problems. It started out being a part of MUA Nevis and then broke off to become its own free standing medical school.
If you have a choice, pick MUA Nevis over MUA Belize. You will be much happier.