Uzumaki

Masterpiece, only sold short by its abrupt ending.
There's so much to talk about in this particular omnibus (only the second horror manga I've ever read) - body horror, cannibalism, and so on - that you must read it to believe it. A small coastal town in Japan is cursed (hence the name, which means spiral in Japanese), and everything goes to hell. There are short stories on everything - such as mosquitoes (whose flying pattern is similar), snails (with the shape of their backs), and even tornadoes.
There's little to no characterization here, and I didn't know beforehand that this was a loose collection of short stories with a joining narrative, but that didn't detract from my immersion. There are the usual tropes here - a slightly unhinged deuteragonist with a gory past, the protagonist who's somehow not affected by the mania happening, and so on. Where Uzumaki shines is in creating a sense of helplessness - at no point do you feel that the characters are in control of what's happening, and this is different from the horror we're used to (the main character saving the day). I'd recommend this only for second-hand helplessness if nothing else.

I read Gyo and this within 28 hours and I need help xD

I found Gyo more “enjoyable” if that's a word you can use with art like this. But don't ask me which was more terrifying. I've never read or seen better horror, this is absolute madness. I don't think written word and my imagination can compare to this. Movies for some reason can't do it justice either. Manga/comic book is perfect for this and Ito is absolute madman. People compare him to Stephen King but that's not right. This is H.P. Lovecraft squared. King has never terrified me in this way. While he's a master of personal horror Ito is king (pun intended) of cosmic horror.