This is a segue of discussion from the Batgirl #12 thread that I think could warrant a more in depth discussion. The issue to point was some debating that the current writer of Batgirl Ms. Gail Simone simply stating that Charise Carnes, aka Knightfall, is defacto Batgirl's primary archnemesis simply makes this so. Conversely others point out that the formation of a primary rogue takes time organically and takes multiple confrontations to be able to determine if that villian is indeed a good fit for that particular protagonist to be a reoccurring foil for the long haul.
Personally for me Knightfall so far has run kind of flat in terms of inspiring interest. The character so far is just so cliche and lacking in menace, despite her penchant/fetish for torture. That and the outfit is straight out generic 1990's at it's most lame, IMO. I just so far am not seeing "#1 archnemesis" written on this character, she's almost as forgettable as Mirror. Conversely isn't the obvious elephant in the room that the Joker is Batgirl's #1 archnemesis? Anyone familiar with Batgirl knows what was done to her in The Killing Joke and the subsequent aftermath.
IMO the Joker himself wouldn't even need to show up here as by proxy Harley Quinn could fill in for him quite nicely, and also has the added benefit of being a victim herself who in turn lashes out at the world in turn, which fits the overall narrative by Ms. Simone to a 'T' per all the villians that have shown up so far:
This gives Batgirl her own villian that is associated with the Joker, and Harley herself is a proven and popular commodity that would help sales for issues with her appearances.
Well Harley Quinn is my top pick, but I also provided a poll of both Batgirl specific and Batman rogues to choose from. Let's discuss!