my favorite season of Supernatural is all seasons. I'm such a big fan that I can choose a season that is my favorite. but show I had to choose it would have been season 10 and 11 because when fighting Sam and Dean back together as a team and not alone <3
Season 5 by far. For the simple fact this season seems to be when the characters are fully developed. Castiel starting developing his unintentional sense of humor. By far the funniest, best story line and of course good action.