Probably Claymore, but the manga are so vastly different that it's hard to compare them like that...
Claymore, Deadman Wonderland, Bloody Monday, Vagabond, Vinland Saga, Battle Royale, Gantz, Apocalypse no Toride, BTOOOM!, etc are all amazing manga in their own right and most are lesser known manga.
The world setting feels alive, stuff is actually happening everywhere, not just where the MC's are.
The cast of characters is absolutely the biggest I seen in any manga, it's just humongous, and everyone has their part to play.
Beside the adventure, the humor that does not feel forced it's also quite suspensfull and has alot of mystery (void century,poneglyps)
The world is inhabited by varies different species like giants, dwarfs, Fishman, humans and a variety of animals that can grow the size of Islands even. It's my nr1 manga for sure
My favourite of all time is Tokyo Ghoul as well as its sequel. The characters are awesome, the plot is complicated yet solid, its MC is a really interesting fellow and each chapter satisfies me completely.
Rurouni Kenshin. I read it when I was younger, I love the Samurai and Meiji era, the story is amazing, the characters are well developed, cool fights and cool villains
Rurouni Kenshin. I read it when I was younger, I love the Samurai and Meiji era, the story is amazing, the characters are well developed, cool fights and cool villains