Consistency is more important.
Could you, please elaborate on this a little more ? I just do not see why the "left" side of the page should be the "preferred" one ! I think that most people pay more attention on the right of two open pages of an open book, or on the right side of one page, because they are right-handed. That is why advertising at the right side of pages costs more.
My reasoning/conjecture here is because most cultures read from left to right, the left side of the page, the side that is scanned
first, should be where the priority image is placed. Similarly, if images were to be oriented on the page from top to bottom, the priority image should be given the top position.
It's not a big deal, but whatever positioning theme is chosen, it should remain consistent across that particular document.