The eternal, unanswerable question.
Basically UCD and DIT offer very similar courses, as do all the colleges given the requirments of the RIAI. The fact that UCD is recognised by the RIBA isn't a huge factor, the reality is that with EU Directives on equivilancy that's not somethign you should worry about, any RIAI recognised qualification is recognised in the EU. Bear in mind that the newer courses are not recognised as far as I know, not that there is any reason that they won't be as soon as they have graduates.
DIT and UCD have slightly different approaches to architecture and there are pluses and minuses to both. UCD is a bit more theory and philosophy based while DIT is a bit more practice and (I hate to say it) reality based. It may seem a bit harsh to say now but I don't think it really makes much of a difference what you think you want to go into as the learning curve is so steep when you first join any school of architecture that everything you thought before hand is pretty much irrelevant.
Otherwise UCD have a much better library but are miles out in Clonskeagh. I personally love being in the city centre every day. Also if you are not 100% sure of what you're getting into the fact that you have a BSc in Arch after 3 years is a nice cushion to carry into another school or area.
If I were you I would call the schools and find out when there are Crits (preferably big crits for first or second year) and go have a look and a walk about. Architecture students are generally dying to be distracted and the studios and crits in DIT are open for anyone to come see.