Personally it would be claymore, often hailed as a female centric berserk.
A story about the lowest class of a generation of engineered superhuman woman fighting monsters to save humanity.
The art gets better and better as it goes on, with stunning panels everywhere(example below).
The intrigue struggle and strive the characters go through is a stellar example of simple yet effective storytelling.
Great Teacher Onizuka
Claymore is fantastic. It's one of those series where you get to see the mangaka MASSIVELY grow as both an artist and storyteller through the course of the series.
I used some panels from the series as phone wallpapers for a while.
My pick is Dungeon Meshi (which will surprise no-one who frequents !dungeonmeshi@ani.social).
In contrast to Claymore, Dungeon Meshi starts off fully developed. Having read it, I am near certain that Ryoko Kui knew exactly where she wanted the story to go, what she wanted it to say, and who her characters are, even as she was drawing up page one.
Despite the humorous premise, and at times light-hearted tone, Dungeon Meshi strikes deep and hard at what it means to be alive. And it does so in general. Not specifically, like about love, war, or the like.
It's not even just about food.
It explores what it means to be young. To grow old. To be hungry. To be sated. The be understood or misunderstood. To do good. To do evil. To desire or be disgusted. To exist.
The characters are oceans deep, and the world is as wide as outer space.
And this despite having a core cast of five, a massive supporting cast that only appears in passing, and a story entirely taking place within one single dungeon, and the tiny island on which it is located.
Oh and it's also probably the best fantasy story ever told.
Akumetsu
Claymore is Amazing! I loved it when I read it, maybe I'll read it again sometime....
Anyway, my recommendation would be Planetes, from the creator of Vinland Saga, a story about space exploration and it's relation with humanity itself, is really beautiful...
Maybe I'll this one again too lol
Oyasumi Punpun (Goodnight Punpun) is a cross-section of a boy's life, who was raised in fucked up circumstances and showcases the horrific consequences it can have going into adulthood. Be warned, it qualifies for nearly every trigger warning under the sun: >!suicide, emotional abuse, a wide range of violence, arson, sex crimes against adults and minors, other borderline sex crimes, parental abuse (physical + emotional), domestic assault!<...
It's a great 'slice of life', but it is truly disturbing. And it's disturbing in a way that no amount of gore and violence could achieve...because you watch Punpun grow up, and he feels like someone you may have known or may have been. You'll have so much sympathy for Punpun...and he will test that sympathy.
Oh, and the art is phenomenal. The stylistic choice to render the main character and his family as cartoonish birds was brilliant, and the art in general is fantastic.
Alternate recommendation that won't sacrifice your emotional well-being for the sake of good storytelling:
One Punch Man is a shockingly good read. It's not exactly an earth shattering narrative like Goodnight Punpun, but it is equally a one-of-a-kind manga/anime.
You wouldn't think a story where the protagonist is effectively invincible and seemingly infinitely powerful would be interesting, but they do A LOT with the premise. The action is great, but the side-characters really form the meat of the story, and there's a lot of genuinely wholesome, funny, and sometimes sad moments.
The anime is very faithful to the manga, so I recommend them both. However the anime is very far behind in the story, so you'll inevitably end up reading the manga if you enjoy the story.
Yokohama Kaidashi Kikou is maybe not your typical recommendation, but very laid back.
I come and re read this every year. The quitensensial laid back manga.
100 Bullets
Nausicaä
Death note
Came here to say the same.
Dragonhead