If I remember correctly, there are 4 people who want Kiddo dead:
Vernita's daughter Niki, Elle Driver(who lost both eyes), Sofie Fatale(lost both arms…well in the original edit), and Gogo's sister(read somewhere that the ice cream truck sound in the beginning of Vol 1 was her stalking Kiddo).

For me: Legend of Korra. And being the backwards person that I am, I still need to watch Avatar: The Last Airbender…