Both take an opposing viewpoint, the one written by a Nord says Alduin is basically a big dragon and Akatosh is something else entirely, and the one written by an Imperial says Alduin obviously is Akatosh and the Nords just misunderstood.
There really isnt much to go on either way in the game that I have found.
I need to do the main quest a few more times, particulary the dialogue with Paarthurnax.