There’s no real definitive answer to this as you cannot predict the economy and hence interest rates. So it’s just a matter of taking some views and deciding what sits best with you.
My view is that with the slightly weakening European and US economy i don’t see interest rates going up in the short-term. Hard to say if they’ll go down or just stay the same. I also think there is quote a bit of discussion about how high mortgage rates are in Ireland compared to the rest of Europe. This may come to nothing, or action could be taken to encourage them down rapidly. Either way, doesn’t seem like an increase is likely. So personally I’m happy taking shorter fixed terms to get the best interest rate available, as I’m assuming that at the end of a 1-2 year fixed term rates will be similar or lower. Fixing for longer at a higher rate would not feel right to me in this scenario.
One caveat here though is if your budget is tight, then the certainty of a fixed amount per month for 3-5 years may work better for you.