I prefer Violet or Lucia.
To me, Isla (although really pretty), is one of those names that was once totally obscure (at least in the US) and is now becoming popular. That to me signifies that it's only going to become even more popular. I also think names like this sound not so fresh and interesting after they peak (which I believe Isla has yet to do). I could be totally off base here, but I have a feeling if you do use a name like this you will tire of it quickly.
Just my two cents.