In your opinion, how would you rank the importance of all the major quest lines in skyrim? This includes The Main quest, Companions, Dark brotherhood, Thieves guild, College of winterhold, the civil war quest line, Dragonborn and Dawnguard.
I believe that the most important quest lines would have to be the Main quest, because alduin seems like the biggest threat (lore wise, at least)
The Main Quest obviously is the most important of the questlines. If left unchecked, Alduin may literally become the World Eater. Second to that would have to be the Dark Brotherhood. With the assassination of the Emperor they have once again become a large dark force in the world. The Civil War would likely come next, but it is very closely followed by the College of Winterhold questline (with the finding og the Eye and Staff of Magnus and the return of the Psiijic order). After these four, the rest seem to be trivial.