Pokemon - Mewtwo or Mew! They've long been my favorites. It would just depend on if I wanted to play an angstbucket or an adorable playful jokester. Digimon - Is Renamon too cliche? I don't care. She's cool. Animorphs - Cassie! I haven't read the series, but she sounds like a big ol' tree hugger and I am sympathetic to this worldview. Discworld - Angua von Überwald! Or maybe Nanny Ogg because clearly panfandom RP needs incredibly pervy old motherly sorts.