I have a PRSA with Davy, invested in an ETF. (IUSQ which is the Frankfurt (euro) listing of SSAC/ISAC. I chose it so I could include emerging markets without the hassle of having to rebalance my portfolio while availing of a low TER (0.2%). I believe it excludes small caps so is somewhat less diversified than the Vanguard equivalent. For me, I wanted as much diversification as I could get while keeping it as simple as possible.
I can’t tell you which of those three options is the best choice, but I would like to point out that it might not always be most cost effective to choose ETFs on the UK and Irish exchanges. The reason I opted for the Frankfurt exchange was the simplification of having it in euro. I know the underlying fund is in dollars but a currency conversion charge appears to be levied by Davy for non-euro listings. It looks to be around 0.7% when you use their calculator that estimates charges. But then again, their estimate of the overseas charge is always around 0.14% but on an actual trade, I found it to be 0.06% so take the estimates they give with a pinch of salt.
If you’re investing smaller amounts, the €25 custody charge will have a bigger impact, so sticking with the UK and Irish exchanges makes more sense. Otherwise, it might be worth getting clarity from them on their currency conversion charges as it may be both cheaper and more convenient to hold a particular ETF in euro.