[Opinions] I prefer Fionnuala
Fionnuala - You get the more interesting, pretty Celtic flavour of the name but not the potentially confusing 'gh' of Fionnghuala and the long string of consonants that kind of clutter up the name ('nngh').
By the way, are you pronouncing all of these names "Finola"? I used to know a Fionnghuala and she pronounced it "Finoola".