With so much amazing anime and manga out there, a person can only reasonably expect to watch and read a small percentage of it. Sometimes, you have to choose whether you're going to experience a series as a manga or as an anime. In some cases, the two are equally high quality, and the choice comes down to what's more convenient for you. But there are also a lot of anime you should skip for the manga.
Often, these underwhelming anime could have been great, but they never finished fully adapting the manga's storyline, which means that relying on the anime alone will result in an unsatisfactory viewing experience. This is the case with Btooom!, Deadman Wonderland, Wandering Son, Gangsta, and more. Sometimes, the story not only didn't finish, it also left out tons of interesting information - A Centaur's Life is so much more complex than the anime gives it credit for! Then there are anime like One Piece that are genuinely enjoyable, but are so long that you might be better off reading the manga if you're a new fan who wants to understand the series without taking on what is basically a part time job.
Which of these anime would you skip in favor of the manga?
The manga and anime versions of Tokyo Ghoul are wildly different entities, and while there's benefit to experiencing both, you should pick the manga if you can only choose one. The reason is Tokyo Ghoul √A, the second season of the series.
Tokyo Ghoul √A makes some major changes to the original series. In the manga, Ken Kaneki continues to fight against Aogiri tree, but in the anime he teams up with them instead. A departure from the source materail isn't necessarily a bad thing, but it's a major risk that in this case, did not pay off. The season was rushed, confusing, and more focused on cool fight scenes than on setting up the reason behind them.
If you want to have a clear idea of what Tokyo Ghoul is supposed to be, skip out on √A and just read the manga.
Deadman Wonderland has a great premise, and if it had actually finished its story and delivered on that premise, it might have stood out as one of the best anime of the 2000s. The anime brings viewers into the terrifying world of the Deadman Prison, where vicious criminals compete in life-threatening games for their audiences' pleasure. When Ganta Igarashi's class is taken out during a visit, he's blamed for it and sentenced to the prison. What's more, the person who is actually responsible is someone who Ganta has been connected with since childhood.
Sounds cool, right? Sadly, the anime doesn't actually capitalize on its intriguing premise. Rather than resolve its many dangling plot threads, the show just peters off into nothingness and doesn't provide a satisfying resolution. By reading the manga, you'll get everything good about the anime while also experiencing a fully realized story.
With one series that aired in the 1990s, a series of movies, and a sequel that didn't air until 2016, Berserk can be a confusing series for anime viewers to get a handle on. Even if you watch every bit of animated material the series has to offer, you're not going to get the whole story - much of it is skipped. If you've read the manga already, you can fill in the gaps, but without the background the anime can be a bit baffling.
Worse, while the '90s series was well done, the CGI animation used in the 2016 sequel was visually unpleasant. While most of the more bizarre looking animation was cleaned up in the Blu-Ray release, the fact that it ever looked as creepy and unnatural as it did in the TV release is hard to ignore. Truly, you're better off just reading the manga if you want to jump into the dark and violent world of Berserk.
Rosario + Vampire is often described as a directionless, fanservicey anime. This isn't inherently a problem - fanservice is popular for a reason - but even the most diehard fanservice aficionado is usually looking for more than just that in their anime experience. The manga provides more. Characters who are flat in the anime have detailed backstories and complex motivations, and the sketchy plot is significantly better developed. What's more, the series actually comes to a satisfying conclusion.
If you really love sexy monster girls, watching the anime could still be fun - but if you want to really understand those monster girls, read the manga.