If you are close enough, you should visit both places and talk to students there, and just visit the campuses/observe life at the colleges, try to get a feel of the atmosphere. Maybe even visit the medicine/health science offices of both places and ask some questions. If this isn't feasible, think about whether you'd want to study under a UK system or Irish system - there isn't too much difference between them, but it seems the Irish system is undergoing a general change at the moment, while UK is still somewhat traditional. Also, think about where you want to practice upon graduating. Again, not too much of a problem going between Ireland and the UK, but if you'd like to stay in the UK, then it might be better to study there. This is a question we can't really answer for you, as it'll be based on your personal preferences.