Don’t read that much manga, only a couple, and is due to the fact that I liked the anime so much I couldn’t just wait. But anime, have watched around 30-40 and for me, it is almost impossible to have a clear top 10 due to the number of titles I like but I know for a FACT these have marked me and are written in stone so far:
Made in Abyss (manga/anime series)
It’s about an adventure into the abyss (a strange, mysterious, unexplored place in the world, where the environment gets harsher as they go deeper). But don’t get fooled by the cute character design. It has serious storyline and some brutal scenes.
JoJo’s Bizarre Adventure (anime series)
There are several JJBA series with different main characters, but they're still related. It’s an action fantasy anime with one strong differentiator: it’s not about getting stronger over and over again to beat the enemy, but instead how to outsmart them. So there’s always some kind of twist in every fight. For an intro, I think JJBA Stardust Crusader might be a good start. Just check some scenes on YouTube.
For Manga, I don’t read that much, but used to like some horror manga like Junji Ito’s Uzumaki, Gyo, Tomie, and so on just because the story is super creepy and fucked up.