User blog comment:Tysonjackson/Big Bad discussions/@comment-11331875-20150530070001/@comment-34924658-20150530162541

In my opinion I look at the Big Bad as that one (or two) villain(s) they are trying to stop this most. For example: Lilith only appeared twice (three but one was a hallucination) in Season 4, yet she was constantly mentioned and no matter how many monsters or villains they faced it still came back to Lilith in the end. As for co-Big Bads (Two or more together is a Big Bad Duumvirate, two or more who aren't working together is a Big Bad Ensemble) I'd say it's the same as Big Bads but now there's two enemies. I haven't even seen season 9 yet but I've seen like one episode and even I can tell Abaddon and Metatron are co Big Bads. As TV Tropes puts it: Abaddon is the main demon enemy they're facing, while Meta is the Angel one.

But anyways. So it seems that Season 1 has a pretty strong consensus. Season 3 and 4 as well (although I still say Ruby for S4. It may have been a plot twist but she played the biggest role other than Lilith.

I think the best person to assume the position in Season 2 is Jake. Then the Demon.

For Season 5 I will say Michael. Although some people consider him and Lucifer a Big Bad Ensemble. If that's the case then I say Meg and Zachariah are the little Bads.