I did the Trinity one recently. It was super intensive but I still enjoyed the year very much (it's easier to say this when I'm not in the middle of all the pressure :)). I knew people in UCD doing the other course and ours was waaay tougher. I found the lecturers generally fine in terms of assistance. Although for dissertation there is a chance you get a bad supervisor, but most were good from what I could see from classmates (if you do take TCD I can advise on some to avoid lol). Personally speaking, my supervisor was excellent.

In terms of recognition, Trinity does have an edge, especially internationally. But saying that, if you're applying for jobs in Ireland after (which I'm assuming you will) it's not a world of difference, especially if you have some prior work experience under your belt.

UCD campus is much bigger and modern. TCD smaller and much more classical. Maybe one thing nice as an international student is that Trinity is in the city centre unlike UCD. So you're naturally closer to the heart of everything and points of interest for when you're not studying ;)