Empire would be the best. As so
1. Empire is semi united though I disagree with what they did to the Alikr.
2. There all that stands between the Jucticiars from just going around and killing all the nords.
3. The empire hates the bloody elves just as much if not more then the stormcloaks.
4. Ulfric stormcloak is and Ignorant, Self justified,power hungry, Racist tyrant and even some nords understand that.
5. In ulfrics dosia you find in the thalmor embasy the the thalmor say that Ulfric being high king would help the Thalmor a lot.