1. Babylon 5
3. Face Off
4. Stranger Things (if a Netflix series counts as TV)
5. Doctor Who
Others close to the top include Lost, Longmire, Hannibal, Under the Dome, Elementary, Quincy, M.E., The Outer Limits (original broadcast series), and Lost in Space (original broadcast series).
Honorable mention to The Curse of Oak Island, not because it's particularly good TV but because I have been fascinated by Oak Island since the 70s when I first learned about it.