If you'd asked me a bit ago, I would've probably said anime, since I honestly haven't read too many mangas. And usually things like action and emotion conveys better into animation than it does simply through illustrations and words. But after I started reading a few mangas due to being impatient, I honestly realise that enjoy both about equally as much, but with certain elements I enjoy more in one or the other.
Like mentioned, things like action and emotional scenes hit much harder in animes. When it comes to action scenes, it's mostly due to how fast paced it is, and it's usually much easier to realise what's actually going on than in mangas. At least in my experience. With emotional scenes, voice acting as well as background music really adds a lot to them, so I definitely prefer them far more there.
In terms of things I favour in the manga though; it's much easier to pay attention to certain details. Since you move along at your own pace, you're not as likely to miss things you otherwise would have in anime. And I often have a bad habit of doing something else while watching an episode of something, so I'm either tabbed away from it and just listening, or just not paying all that much attention to it. And sometimes I just enjoy reading the stuff more.
So yeah, I really like both for different reasons, which is why I'm likely to watch both the manga and anime adaptations of some series :D
I prefer watching it first to be exposed to the anime's world and characters. It's difficult to imagine colors, voices, actions, and backgrounds when reading manga panels. I tried reading manga (that have not been adapted) before. but I couldn't get far with that.
If an anime stopped or diverged paths, then sure, I can pick up with the manga and imagine the scenes in my mind.
Also this pretty much. I feel like it's much better to move from an anime to a manga rather than from manga to anime, since it'd kinda meet the same problems as with moving from subbed to dubbed. You may make up your own voices/perception of characters while reading the manga, and end up disappointed from how it was adapted into the anime, but when going from the anime to the manga you've already been presented with all that.