Both
Anime. There's something amazing about seeing your show live in color and in motion. With sports, you get more drawn into it. With romance, their are nuances with the voices and facial and body movements that convey more in motion. Horror, Action, Slice of Life -- letting it unfold before you is very pleasurable.
Manga. There are many manga that don't get converted to anime (i.e., Cesare, Vinland Saga). Also, many times the anime adaptation is not true to form with the manga (i.e., The Morose Mononokean, Kuroshitsuji). Depending on the series, the manga may offer "more" (whereas by contrast, many times the "extras" in anime are humorous filler episodes). Again, depending on the series. I've seen some anime that have gone more into character development in their "filler/humorous" episodes, which fanfiction lovers like myself enjoy. Also, THE MANGA IS USUALLY WAY AHEAD OF THE ANIME SO YEAH THAT'S A PREFERENCE. I just started watching The Rise of the Shield Hero upon your recommendation and IMMEDIATELY RAN TO THE MANGA when I ran out of episodes (because I want to kill a specific character and you know exactly who I mean).
So I like both for different reasons... Typically with sports, horror, and music-centered genres, I like to watch anime. I like to consume both anime and manga when it comes to romance, high action shounen, and slice-of-life shows. For historical dramas and shows that aren't fully fleshed out in the anime version, I prefer manga.