In my opinion, they both have their legitimate reasons for you to join. I originally intended to join the Stormcloaks due to my character being a strong Nord and against the ban of Talos and Thalmor dictatorship, but Ulfric seems to be a jerk and formed the rebellion just to advance his own ambitions. The reason I joined the Imperials is because I felt a connection between the Septim bloodline of emperors, which were all dragonborn, and my own character, who is also Dragonborn. I don't think the Imperials really had any choice accepting the White-Gold Concordat, and are against the kidnapping of citizens for worshipping Talos. It's the only realy way Skyrim will still be ruled by men, not mer. To me, the Stormcloaks are just motivated by Ulfric's reasons and don't really think through the Imperials' perspective. They are just mere rebels, not freedom-fighters.
I also joined the Imperials cause Jarl Balgruuf seemed like a nice guy, helped me through the whole freaking storyline.
Poll
