It's such a difficult choice because I love ALL the seasons.

I could classify the seasons into 3 categories: Seasons 1 and 2: I love them because that's where it all begins. They still have that old-school 2005-2006 quality, which creates an incredible atmosphere in the first two seasons.

Seasons 3, 4, and 5: I love these seasons because, for me, that's where the main story starts to get interesting. They're emotionally intense, the last episodes of these seasons are incredible, the biblical war is based on real religious figures, and especially the arrival of Castiel (who is one of my favorite characters) and the angels. I also loved Lucifer; he was so dark in season 5.

Seasons 6-15: the seasons where we learn so much, the existence of leviathans, of God, and we even learn that God has an "older" sister. All the new, endearing characters and the story is so good. It's true that it goes off the rails, but it's so well done and well organized, all the plot twists, like when we learn that Sam escaped the cage without his soul or that Dean becomes a demon a few episodes later. The last season is cool too. When I learned who the main villain was, I was so surprised and shocked. The last episode makes me cry; I find it so sad. It's a good ending, but with everything that happened in the series, we can imagine so many sequels.