Not all of the pages have the same purpose. Two of the pages, Facebook and the web site are meant to drive traffic to iTunes and Google Play, depending on the user's device. Google Play and iTunes are meant to drive downloads, so the goal is to get them to the top equally. Amazon also has an Android download, but I'm not trying to drive traffic there.
The one place that I have full control is my web site. Since it will have links to the app stores an argument could be made that this should be the goal for the top rank, but I assume I'd lose significant installs if an extra click is required. In any case, the page would bleed off to the app stores unless I cloaked the link.
Facebook is part of the social viral strategy. I would assume most Facebook traffic would originate from within Facebook.
I may be worth mentioning that all promotional activities will have links to iTunes and Google Play stores. That includes reviews, PR etc.