Empire. First off, I wasn't going to help destroy the empire I helped salvage in Oblivion (admittedly things have changed). Second, Ulfric doesn't really have much ground to stand on. He keeps going on about "Bleeding for an empire that won't bleed for us." Which is immediately contradicted by the fact that the empire has troops in Skyrim as much to protect the citizenry as to stop the civil war. Also, the only thing that anyone seems to be able to point to as a sign of the empire oppressing Skyrim is the White-Gold Concordant, which they didn't really have much say in anyway. Lastly, Skyrim's independence largely benefits only the Thalamor, and fuck those guys.