[name]Oonagh[/name] seems the most traditional/authentic, but I wonder if it will cause constant pronunciation issues? What do you think?
I don’t think it would create any pronunciation issue with the spelling being [name]Oonagh[/name] 
I think [name]Oonagh[/name] looks the least appealing. [name]Oona[/name] is cute but honestly looks a little strange with the double Os. I have to say [name]Una[/name] is my favorite, and I think it’s easy to pronounce.