Then I visited Windhelm and actually met Ulfric, and it turns out the guys a brutal, racist assassin and iron-fisted dictator. And that loading screen that describes how he shouted High King Torygg "nearly to pieces" did not help my opinion of him at all. That, plus realization that if Ulfric succeeds in dividing the empire even further the Thalmor will probably overrun them and conquer the world really makes me want to support the Empire.
I won't say he's not brutal. Markarth proved he is. Guy doesn't say anything racist though. He doesn't bother to send guards to people that don't support his cause. If you side with him, he'll look out for you, otherwise you're going to have to deal with problems yourself.
He didn't shout torygg to pieces. People that were at the duel state he used thu'um(Namely Fus Ro Dah) and then stabbed Torygg through the heart. The nordic tradition is that the strongest can lead. There's no restrictions to methods. Either side could have used magic. If Torygg had known them, shouts would have been acceptable from him too. The thu-um part was a symbolic move on Ulfric's part, Tiber demonstrated his mastery of the voice to the nords as well when he sought to form the empire. Ulfric could have easily beaten Torygg without the shout(He's a war vet and torygg barely has combat experience at all).
Division from the empire isn't a bad thing if the empire isn't able to manage its own forces(As demonstrated during the great war). Not to mention allowing enemy infiltrators to freely study your forces and positions is a big no no. If Great War 2 pops up, both hammerfell and skyrim would ally with the empire despite their spats with them. 3 nations that can manage their forces effectively > 1 nation that bumbles around with its large size. Both the nords and redguards are great sailors, and can provide a good deal of naval harassment and raiding. They're both good warrior races too and can defend themselves. The empire can call on battle mages from High Rock and its own legions. Hopefully they've learned from the first great war and are actually gathering intel of their own on the thalmor activities.
After 80 hours, I still haven't heard a compelling pitch from either side, so I'm staying out of it.
I'd say there was a better case for joining the orcs, on evidence to date...
Join the khajiit. They don't really care for this whole war thing. Give em some skooma and all their troubles drift away.