Xbox One. It's the first version to release, advertising will focus on it, come the PS4 release the XOne version will be a bit cheaper so...yeah, incresaed install base will be outweighed by these factors IMO.
I'm also not convinced that Fallout 4 will cause that much of an issue. Sure it'll delay some purchases (like mine) perhaps but we're talking about lifetime sales so it'll even out in the end.







