I generally prefer the source material to any remakes i.e. books better than movie. While that isn't always true, a few movies are better than the books, One thing I noticed is generally the version I like has less dumbing down of the characters. For example the Ranma manga is better than the Ranma anime. Just about every character is smarter in the manga except for Akane who is smarter in the anime. Gourry is much smarter in the original Slayers novels than he is in the anime, not the manga the manga seems to be based more on the anime than the novels. Even with the dumbing down though Slayers Anime is still my favorite anime. Excel (Excel Saga) is smarter in the manga than the anime (particularly later volumes), Osaka is quite a bit smarter in the manga than the anime (she's still forgetful and spacey though), etc.
Why do they dumb the characters down? The smarter more witty versions are much more interesting. Is it easier to write the characters dumber or do people find dumber characters to be more funny?