Ireland and Australia have equal prestige, in my opinion. International students going there also have the option of being able to stay back to complete internship, get PR or citizenship, and become a doctor or go back to North America in both Ireland and Australia. And there are many who can score high on the USMLE. In fact, from what I've heard from the internationals I've seen studying abroad is that they go abroad because USUALLY (generally, not universally) have high MCAT and low GPA (of course, there are plenty of exceptions, where both are high or both are low and even some with the other way around, but most of these cats go for the Caribbean route). Thus, they can study for the USMLE on their own and because a lot of medical schools have a pass/fail grading system, GPA doesn't really matter anymore so they can focus on acing the USMLE for decent matching stats.
Ireland has always gotten a higher match rate because the students are more dedicated to returning to the United States or Canada while internationals going to Australia may end up choosing Australia over going back. I really don't think it's because either training or quality is better but rather how similar the curriculums are to the US. Australia focuses less on the sciences so I think Ireland has better preparation. EVEN THOUGH I know it's not geared towards the USMLE, Ireland's science background may help students better.
But we can generally agree that the reputation of Ireland or Australia is better than the Caribbean (it's spelled one r and two b's; sorry, couldn't resist 😛). And with equal stats and equally powerful letters of recommendations, Australia or Ireland WILL have BETTER chances of getting into a residency. Because the Caribbean is usually a no-no on any list of medical schools and most will reject you JUST because you're from the Caribbean and nowhere else. And be warned, the discrimination against the Caribbean medical schools are extremely prejudiced. To put it simply, they look at you in distaste when considering you for residency.
HOWEVER, because the Caribbean is actually divided into two polar ends (the best of the Caribbean like SGU or Ross or SABA have up to 88% matching rate even into tough specialties like surgery or emergency medicine WHILE the others like Spartan, etc are not even acknowledged by the US or Canada and are not well acknowledged), they are a bit underestimated in my opinion. Caribbean schools DO train you to take and even ACE the USMLEs and they DO send you to the United States for 2 years for clinical rotations (both essential for a good match), all at the cost of reputation and a bad taste in your mouth for the rest of your life. As for what you want, it depends on your pride and whether you care what's written on a piece of paper.
All I can say is, if you have confidence in your test-taking abilities, you can study alone AND you care a lot about what school to go to, go for Australia or Ireland or England or other famous European schools. If you are horrible at taking tests or need a cram-school style curriculum to take your exams, you really MUST go to America or Canada for residency or bust, and you are willing to sacrifice your reputation for a match, then go for the Caribbean.
That's the general rule of thumb.