Two different titles of Noragami manga, which one should I start? I have seen only the anime. I heard that the manga is still ongoing and that Fujisaka was exposed in it but I was in dilemma when I saw two mangas: one with the name Shuuishuu.

They are both still ongoing and seem original. Which one should I start?
From Wikipedia: 


  Extra chapters of [Noragami]... have been compiled into one volume under the title Noragami Shūishū (ノラガミ拾遺集). Both the main series and spin-off series have been licensed in North America by Kodansha Comics USA, under the title Noragami: Stray God and Noragami: Stray Stories respectively.


Noragami: Stray God (or simply Noragami) is the main series. Noragami: Stray Stories is a spinoff from the same author, Adachitoka.