If you want good fantasy manga, you read Berserk. It's not only one of the best fantasy manga in my opinion, it's also one of the best fantasy stories I've read period. It's dark, it involves and depicts a lot of disturbing things like murder, torture, abuse, war, and rape in an uncaring Medieval European-esque setting, and it never pulls its punches. It doesn't just imply things, it shows them in gruesome detail. But it's not an edgefest and it does not show include these subjects in its narrative just for the sake of being dark, nihilistic like a lot of fantasy stories do because it's anything but; at Berserk's heart is very emotional and human story. Its characters are also amazing; Guts is a fantastic protagonist who develops all throughout the manga's run, but there are plenty of others, major and minor, who also leave an impact. The art is amazing as well, some of the best in the business. Miura was very inspired. He packs a lot of detail and emotion into his illustrations (and boy, did he love making a lot of epic two-page spreads), his paneling allowed the imagery and flow of the story to feel cinematic in a way most comic artists don't accomplish, he was perfectly capable of depicting action with still drawings, and he had some of the vastest and most varied creature designs ever.

Honestly, I'd skip all the anime series; none of them are good (especially the shitty CG ones made in the 2010s), none of them tell the whole story and what they do tell, they remove large swathes of. And no, the moving images do not make up for the utterly detailed majesty of the late Kentaro Miura's art, not when the animation in all of them was so cheap. Even if you do watch them, you're going to have to go to the manga eventually, so you might as well just get to the main course.

As for other sci-fi/fantasy series, Nausicaa of the Valley of the Wind is also fantastic. It was made by Hayao Miyazaki (who was behind the Howl's Moving Castle anime), and tells a morally-nuanced story set in a neat post-apocalyptic world inhabited mostly by large insects and fungal forests that emit spores which are deadly for humans. There was an anime movie based on it which was alright, but it was made before the manga was finished and tells a story that just isn't nearly as epic as the original. Though really, you cannot go wrong with any of Miyazaki's films; just about everything he touches is gold; I personally consider Howl's one of his weaker movies, with the strongest ones being Princess Mononoke and Spirited Away, though even his simpler films like Kiki's Delivery Service and My Neighbor Totoro are worth watching. It should be noted that Howl's Moving Castle was not based on a manga, it was based on a British book by Diana Wynne Jones.

Akira was also great. Both the film and the manga are worth perusing. The former is admittedly simplified from the latter (considering it too was made before the manga was finished), but it opts for telling a generally different story with the same characters, setting, and themes, so it's able to stand on its own just fine as a kind of alternate universe tale.

As for other series, I'd recommend Cowboy Bebop (anime) if you haven't seen it already, Irresponsible Captain Tyler (anime), Battle Angel Alita or Gunnm as it was called in Japan (manga), and Iria: Zeiram the Animation (anime).