I’m going to have to say it’s a tie between Season 7 and Season 11. I didn’t like the whole Leviathan thing from Season 7. I mean it would be fine for 3 episodes, but they just do it for pretty much the whole way through. And that Dick Roman guy really creeps me out. Also, Leviathan Sam and Dean kinda made things even crazier as it already was.
Season 11, well I won’t go into much detail but you won’t like what you see. Trust me.
Least Favorite? Definitely Season 7
My favorite is really hard to nail down. I like alot of Season 1-4. Parts of 5 and 6. Not a big fan of 7 or 8…9 and 10 are good.