Pazzini does have the happy habit of wandering into space.
Gilardino is very good at sneaking in front of his marker and getting a flick to crosses, but he isn't so good at completely losing a marker.
They are also very different in their movement; Gilardino will almost always move to the front post, while Pazzini is move likely to try to peel of behind his marker to the far post.
Different styles, but similar standards of players in my book.
Personally, I like my striker to always be looking to get in in front of his man, so I like Gilardino's movement more than Pazzini's.