I, too, prefer
Orla.
I don't think
Ornella is hideous or anything, and I do like that
Nell is a possible nn, but...there's something about
Ornella that feels funny when I say it. It reminds me a little too much of the words ornament and ornate (come to think of it, that's appropriate since it's more or less an ornate version of
Orla). For some entirely unkonwn reason,
Ornella also reminds me of popcorn.