Well as far as anime goes my Favorit is, has and probily always will be is Sesshomaru!!! But with that said, besides him there's always this guy... he's name is Lucifer.
*(I'm using a fictional version of Lucifer in my manga so its okay to post about him:)
Though he's not really a demon, he's a god/Devil, but... who cares this picture is frikin sweet.
just like sessywind's answer (first anime demon then actual demon) My inayopendelewa is Mizore Shirayuki (a yuki-onna) and Jalyn is a demon who lives in my bedroom. He's very annoying at times but were good friends.
Anime: Sebastian (Black Butler) Manga: Cesare (Cantarella) Book: Julian (Forbidden Game Series) Movie: Blackheart (Ghost Rider) if i told u the names of any of the real 1s I know wewe wouldn't know them so I'm not gonna bother....