everybody's telling me what, but not why
If I were to go into a bit more detail about each of my picks:
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Devilman: My favorite part about the series is the relationship between Akira and Ryo, seeing how it develops as the story changes over from a motw fights against various demons to an anti-war commentary as it shows humanities decay. The series was always quite dark but the final volume or so cranks it up, the series doesn't have a happy ending but one that does stick with you. I think it's a short enough read that you could finish it in an afternoon, though I don't know which version you have as I know some newer ones just haphazardly stitched in Shin Devilman and it ruins the flow of the original series. If you see a sudden shift in artstyle I would honestly just skip until it switches back, most of shin is weird time travel shit (Like going back to see Hitler).
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Vagabond: Follows Musashi Miyamoto as he grows as a person and develops his sword style. It starts out largely focusing on the fights as he proves his strength but later it begins to switch more into discussion about what strength actually is as Musashi starts to go up against people far stronger than his raw talent can beat. I'll say that if you're someone that read Vinland Saga and hated Farmland arc you'll probably also dislike Vagabond as it has a very similar arc full of introspection for Musashi on
what does he really want. There's also technically no ending besides an illustration the author drew a while after the series went on hiatus, but it's still worth reading for the beautiful art (Slam Dunk author) and its captivating story (I personally really like Musashi's character growth but I also really liked Thorfinn's growth from Edgy boy).
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Holyland: Series focuses on MC Yu as he gets into street fighting but the larger focuses is on themes like Depression, finding your place in society, and the outcome of violence. I enjoyed the fights but my main enjoyment of the series was reading the authors commentary and discussions, it felt like the author himself had a lot of experience with the things that happened. Fights also tend to be more on the realistic side, nothing like what you might get in something like Baki, but discussions things like Knife fights or how scary Judo is in a street fight setting. Holyland is probably one of my favorite manga of all time and I'll give it a re-read every so often, the art is something you get used to though I can see first time readers not enjoying it. Your pile also had his other works like suicide island and Taiga which I would check out if you end up liking Holyland, both are pretty decent though not as good as Holyland.
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Nobunaga's Chef: Chef with head trauma finds himself back in time and ends up becoming a chef for Nobunaga, he doesn't remember much about himself but his knowledge of western cuisine remains. I'm a big fan of both historical and cooking manga so it was really no surprise I ended up liking it, it delivers well on both fronts. I guess if neither of those things interest you then you can probably just skip the series, that's pretty much what it has going for it.
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Summit of the Gods: As I haven't read this one myself I'm mainly basing it off of what I've heard about it and the author's other works that I've read. Basic premise is a photographer finds a camera that apparently belonged to the missing George Mallory, a climber that went missing on Mount Everest, photographer then goes on a climbing adventure with his friend based around this. The author, Jiro Taniguchi, is fairly famous (at least in france where most of his works have been released, was even knighted) and the works of his that I've checked out have been very enjoyable down-to-earth works. There's something really appealing about his artwork.
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Gundam the Origin: Already kind of went over this one but if you aren't adverse to mecha it's a pretty interesting story of war between two fairly fleshed out factions. It also focuses quite a bit of time detailing char's past and what exactly is driving his actions during the war, something that was somewhat skimmed over in the actual series. I'm pretty biased towards this work given my love of Universal century gundam but I'd say Origin is a pretty good story by itself.
I don't know if any of that helps a bit, it's been a while since I read any of these works so I'd have trouble giving a detailed plot description.