my 8 year old dd is Iris, so i love that a lot. Ivy is also nice too, but i do know a few little Ivys under 6 and no Iris', if that makes a difference.
Iris sounds stronger and more elegant to me, and has a great namesake in Murdoch (one od my all time favourites), and these are the reasons we chose the name (aswell as it being a family name)
Ivy is lovely, but not as pretty or powerful!
Crikey - i do talk rubbish - but i know what i mean!