Stormcloask all the way, they're the only ones actively bothering to even do anything about the Thalmor. The Empire is just letting those little Elven shits walk all over them in spite of the Thalmor having absolutely no bite to back up their bark with. The only reason they can even do anything in the Empire or Skyrim is because the Empire are cowards and being a door mat. The Great War was just as damaging and harmful to the Thalmor as it was to the Empire, if not more so. The invasion army that they launched into Cyrodil was the largest army ever fielded in the history of Elven kind or in any of the incarnations of the Aldmeri Dominion......and it was destroyed almost down to the last man. The invasion force into Hammerfell fared little better, the Red Guards killed most of them and a bunch more died while the Thalmor fled across the Alik'r desert. And seeing as the Elves have always reproduced much more slowly than humans, they're going to take far longer to recover than the Empire will. The Stormcloaks are the only acceptable answer for me. The Empire is too chicken to dare so much as looking as the Thalmor wrong or even sneeze in their direction when they have absolutely no reason to be.