I don't like the empire because they seem to me as if they are the Thalmors lap dogs. Which makes things very awkward for me because at the same time, I'm a an Altmer (albeit I consider myself separate to the ways of the Thalmer).
That aside, helping Ulfric really doesn't make sense, considering the Dunmer live in the slums of Windhelm, and if I remember rightly Argonians aren't even allowed in the city. I've also heard a couple of characters talk about how little Ulfric thinks of anybody but Nords.
So in my opinion neither the Imperials or Stormcloaks deserve to be in power. Which possibly opens the door for Paarthurnax, however it seems unrealistic that he would become the ruler of Skyrim for two reasons. Reason one, everybody is fearful of the dragons so having a dragon ruling, even though he is peaceful like a monk in many ways just wouldn't work.
Reason two, Paarthurnax talks about the problems he had controlling his power, and how he hopes he will never return to the way he was. That is why he stays in Solitude on the throat of the world. He wouldn't accept the role, it would be out of character for him to do so.
Perhaps the Greybeards could be in with a shout, they are after all servants of Paarthurnax.