I do enjoy both and I LOVED Rebecca's Destiny version.
I know a couple of people that watched Destiny and that song was their favorite. They weren't avid Celtic Woman fans prior to Destiny, but they said the girl playing the harp in Destiny was their favorite Celtic Woman...
No they weren't talking about Tara in this particular case, but that would have been AWESOME!
Anyways, as amazing as Rebecca's version was, I can't vote against Orla, in this case. Orla is amazing and Isle of Inisfree is one of my favorite Orla songs.