Though this segment is called Fix or Nix, I am loath to recommend nixing Supernatural. I've been watching Sam and Dean Winchester send demons back to hell since '05, and its worst episodes still have a decent mix of wit and action.
Still, I feel it needs some kind of reboot, echoing as it does some of the plot fatigue that plagued Buffy the Vampire Slayer by the end. Both series played their trump cards early -- as if they expected to be cancelled tomorrow. In season one, Buffy fought and defeated the King of the Vampires, a.k.a. The Master. Subsequent seasons required bigger and badder villains than the last (Caleb, the god Glory), kind of a cheat when you're claiming each new villain is the worst imaginable.
In Supernatural, Sam and Dean (Jared Padalecki and Jensen Ackles) started by thwarting the apocalypse and sending Lucifer (Mark Pellegrino) back to H-E-Double-Hockey-Sticks.