Showtime’s flagship series Dexter returns for an eighth and final season this weekend, mostly limping to the finish line after a brilliant start and some strong work along the way. Weep not, serial killer aficionados: There is an heir to this gory throne, and it’s NBC’s Hannibal. It’s even more twisted than Dexter, if that’s possible. How else do they differ? Let us compare TV’s most revered murderers, from killing style to creepiness to love of art-directed murder scenes.