I prefer Manga for the most part. Sometimes I like to see something animated if it is REALLY well animated, and faithful to the source material, but will always prefer the original art form.
Especially if the anime doesn't look as good as the Manga, like One Piece. I love the story, but the anime is not nearly as good as the manga in multiple different ways same goes for berserk and some other animes.
The manga has more brutal events for the first case. Panels that were shocking and impactful were reduced to make them less disturbing for mainstream audiences.