List.empty vs. List() vs. new List()

First of all, new List() won’t work, since the List class is abstract. The other two options are defined as follows in the List object:

override def empty[A]: List[A] = Nil
override def apply[A](xs: A*): List[A] = xs.toList

I.e., they’re essentially equivalent, so it’s mostly a matter of style. I prefer to use empty because I find it clearer, and it cuts down on parentheses.