Okay so Ghost Hunt is by far not perfect in any way but it is definitely one of my favorite mangas. This series has a completely different vibe than any other manga I've read (To be fair I actually haven't read a ton) and the anime adaptation also carries this vibe.
To begin with the team of characters that the story follows all have equally interesting and important roles, even though Mai and Naru are the main two. Mai is personally the most relatable and through her we are able to learn more and more about the world of paranormal investigation.
All of the stories in the manga are filled with interesting lore from various cultures and extremely creative plots that never once seemed repetitive to me.
The thing that really got me was the idea that the manga got across, especially at the end. The anime is interesting and a good way to pass time but after reading the manga, everything really does come together and the ending is a message that I will never forget.
IMO you could read the manga and then watch the anime if you really wanted to but I watched the anime first. This is what sparked my interest in Ghost Hunt to begin with and led me to the manga. Considering that the anime does not have the last couple of volumes of the manga, I think it's a perfect way to start.