I go to UCD. I know that Manchester is a very highly ranked university, so that might be important to consider. As far as the cities are concerned, I have never been to Manchester city centre, only outside it, and I cant say I have heard anything spectacular about it. Dublin on the other hand is a very quintessential European city imo, although rent prices are extremely high (average 1,000 euros per month even with University accommodation). The up-side is that UCD is the best university in Ireland (alongside TCD) and I am pretty sure it is very strong in data science. With a lottttt of tech companies and corporate firms here, it's also a strong city to go job- or internship-seeking. I know that UCD graduates fill the Goldman Sachs, JP Morgan, Google, Amazon, etc., jobs here in Dublin. The only thing is that internationally, I think Manchester is more prestigious. I would say look at the overall costs and judge from there. Other than that, UCD is a fantastic modern campus (although I would have preferred it to be old, as I study history, but whatever) with everything you need. We often describe it as a town within a city. There is a huge sports centre with like 500 football fields, tennis courts, olympic pool, around 900 gyms and ... you get the picture. The main library is quite big and there are around 8 university residences with accommodation ranging from studios and shared rooms to apartments with ensuites and shared bathrooms. Let me know if you have any questions on UCD - I've been here for a few years and am graduating soon.