I usually prefer watching or reading a show in the original form it was released, book, manga, anime, whatever. The new creation can be valid and good on its own, but for the definitive take on the story, one should look at the original.
In anime and manga, this is quite important. We all know how some shows begin serialization before the original story is finished, and thus have to not only change things, but make up a lot of it as they go along (Fullmetal Alchemist), or that they descend into more and more “Filler episodes” of original and usually subpar material (such as Naruto and Bleach). But sometimes they go beyond.