Since people's palates differ widely (witness all those posts from the "picky eaters" or the "bland eaters"), there is no hands down "best" type of restaurant of any kind at WDW.
That being said, my favorite Italian place is Il Mulino. It's expensive and I am sure a relatively small number of people on these boards have tried it, but it is very high quality and delicious Italian food (with wonderful service as well).