I personally don't like using characters from television shows or anime or books or video games, I just find it too difficult. I don't like being tied to that characters personality, and I feel awkward replying as a well established charcater, because everyone has their own views of how that charcater should reply, but with an original character, you have a load of wiggle room, because you made the character and you know what they should do.
The only charcater I use who is based of canon is Wilson Maxwell, based of Wilson from Don't Starve. Even then, the only stuff I use is the fact that he is a science guy, and he goes insane in the dark. The fact that Wilson has little to no personality in the game, Don't Starve being rouge-like, let's me determine his personality.
And I'm not too find of playing with people's canon charcaters because they use the lore from whatever series it is from, and I'm not always well acquainted with it. Another reason is that, let's face it, every character is overpowered in their series, at least one time, and I find that people tend to bring this one moment of "over nine-thousand" into the role play every few posts.
I may have got a bit off topic, but that's my thoughts on it all.