@Dibullba True, it is interesting. I'd imagine that it would probably rely on that person's preferences and experience with anime/manga/novels in general. I love to read novels because of how I am able to almost freely shape the world/characters in a manner that I see fit. With manga, you have to accept the mangaka's design and environment (same with animators). When one tries to adapt the other (let's say manga to anime for now), a few liberties end up being taken. Some art styles end up changing. Sometimes it is due to low/high budget, other times it is due to the difficulty of animating a certain art style. Sometimes the animators/directors simply want to use something different. And there are times where the change is good, but other times the artistic choices end up (possibly) burying a great storyline. Aku no Hana is a great example. I remember the outrage over how different everything looked from the manga, and the ratings for it proceeded to drop at an extreme rate in the beginning. The ones who did stick around found that the story was still great despite the art style. Something similar almost happened with Shinsekai yori, where some people thought that the anime was based off of the manga (which is extremely gratuitous with romantic scenes) and didn't consider watching it for fear of it just being another hentai/ecchi type show in disguise. That's not to say that there haven't been any successful adaptations (There have been plenty), but the bad can sometimes cloud the good that has happened. In my opinion, the reason that novel->anime transitions seem superior lies within the lack of art (if no one has a set standard for what it should look like, theoretically the person should be able to pay attention to the story instead of the differences in art style). At the very least with a novel, the most that a reader can focus on is the story (maybe the cover art if available), however the combination of art and story can change a person's perspective drastically. Or at least that is just my two cents on the matter.
This actually reminds me of this one other series that is available in novel (or was it light novel...), manga and anime. Each medium may have the same title and story (at least in the beginning anyway) but are told from different time perspectives. It dealt with time travel. I think it went something like the manga version dealt with the past, the anime the present time and the novel the future. I might have gotten them mixed up a little, but the point is that each medium was released at the same time. So technically you have 3 different storylines, and no real way to compare the three since they each have a different story. I wonder how that series went....If I find the name I'll edit this post.
"A reader lives a thousand lives, the man who never reads lives only one." - George R.R. Martin