Siding with the Stormcloaks. When I first played Skyrim, I started with siding with the Stormcloaks, it seemed right based on the limited info I had at the time. But after trying to get my "Imperial playthrough" out of the way, visiting each Jarl so I could become Thane in each hold, I got to see the consequences of siding with the Stormcloaks. Then when I read the Thalmor dossier on Ulfric and learned that Ulfric used to work for the Thalmor, I said "What a jerk I was!".