I strongly disagree with this based on what I've picked up on. Apparently the Stormcloaks are a rebel faction. This tells me that they're the good guys automatically. Think about every story you've ever read involving a rebelion. Rebels are NEVER the bad guys! No one rebels from the land of puppy dogs and sugar frogs! The Legion is probably an oppressive government filled with corrupt tyrants. Also, look back to Fallout: New Vegas, the Legion was the "evil" faction.
Now I'm rambling about something I know very little about but this is my opinion based on what I've heard through discussions I've seen here on the forums. If I'm wrong about something or if you agree with something I've said go ahead and leave a comment because I want to see everyones thoughts and opinions on this. And if anyone can give me a link to a topic describing IN DETAIL the motives and basic traits of both factions I would be very greatful.
Also, I'm hoping personally that one factions good and one's evil so that there can be a neutral ending. (Like in New Vegas, where the courier takes over for himself.)