User blog comment:DarkSaiyanMitsubi/Empire or Stormcloaks?/@comment-1080767-20121010052737

Depends. If you're trying to be a Thalmor spy, then join up with the Stormcloaks. That way, the Empire loses support and is easier to topple. Moreover, Skyrim itself will have no unity with other provinces, so when Cyrodiil falls, Skyrim can be attacked from other directions besides the borders to Cyrodiil. And while you're at it, become a respected member of the Stormcloaks, allowing the Nords under you to place faith in you, as well as ingenuous trust from Ulfric himself. Niranye did it, that is she got the respect of her people as an Altmer. Moreover, the Empire is your rival and is the priority target, not the people of Skyrim who are about as isolated from the Summerset Isles as possibly desirable.

If you're an outright Thalmor advocate and officer, you would logically have a place in the Empire, clearly not in the ranks of the Stormcloaks. You probably hate Ulfric and his blasphemous Talos-loving soldiers and their primitive heathen traditions.