Saiyuki by Kazuya Minekura. A Fantasy manga rated Older Teen, published in English by Tokyopop.

Loosely inspired by Journey to the West. The foul-mouthed, chain-smoking monk Genjo Sanzo is ordered to travel west with three demon companions, Goku, Gojyo and Hakkai, to stop a sinister plot to resurrect the demon lord Gyumaoh.