Which Option for P2, International or Ireland/UK

No! There's no chance that I can answer that! For one thing, your question is far too vague. "Best" - what do you mean by "best" as in "best for the P2 exam" and "best" for what? Both variants are equally difficult. The UK is only slowly adopting the IFRS whereas the international variant is based on the IFRS. This means that UK students are having to learn the difference between the UK standards and the IFRS whereas non-UK students are learning only IFRS. So probably the UK variant is better because you learn more and are thus better educated!

I would like to choose which variant to take if I need to have a UK practicing certificate upon completion of my ACCA studies?

Then it's got to be UK variant - unless you delay until the time when, eventually, the UK fully adopts IFRS and moves totally away from their own standards