[Opinions] Guess which one I prefer? ;)
Obviously Isla. The only downsides to the name, for me, are spelling and pronunciation issues. But with the popularity of Isla Fisher and with the name hitting the Top 1000 so high last year (came in for the first time ever and in the 600s), I'd say it might not be quite so obscure in the next couple of years. However, I don't think we need to worry about it hitting the top 20, either. This is all assuming you're in the U.S., btw.
Georgia is gorgeous as well. Not really many downsides to it, except her being called Georgia Peach or something, lol. I just greatly prefer Isla.
Good luck.