For me, best manga ever is very easily Takehiko Innoue's Vagabond. As long as you don't have some kind of dislike for samurai or violence, I can almost guarantee you that you will love Vagabond. Amazing artwork, compelling story, partly historical, a lot of great philosophy and spiritualism, good pacing...just a wonderful comic. WARNING: After reading the first half of Vagabond, fight scenes in other manga will just seem lame and sterile in comparison. Also, Innoue has released gorgeous black and white and full color art books with scenes from the series. It is magnificent.