Any ghost-related books that resonates with you can be good ghost hunting books. My judgment is subjective, based on my experiences in this field.
In other words, if you’re looking for ghost stories – fictional or true – that can be a matter of taste.
Nonfiction
– For years, I’ve been an almost rabid fan of Colin Wilson’s books. Though I don’t always agree with him, I’m dazzled by his innovative ideas and research. He’s an “everything but the kitchen sink” kind of guy.
– I like the ghost hunting books by Jason Hawes and Grant Wilson, because I know them.
So, I understand the context of what they’re describing with each story and case.
– Troy Taylor’s book, The Ghost Hunters Guidebook, is superb for beginners.
– I like the speculation in Marie Jones’ book, PSIence.
– Michelle Belanger may be my favorite authority on paranormal topics, but I’m biased. Michelle is a friend, and I’m always impressed when someone has read more books than I have. (I’m pretty sure she has.)
– I love the insights and humor provided by Lesley Marden’s book, Medium, Rare.
And, of course, I’m proud of my own books. My most popular book is 
Ghost Hunting in Haunted Cemeteries. (It’s free to read in Kindle Unlimited.)
Folklore and Fiction
– Since childhood, my favorite ghost stories have been those by Edward Rowe Snow. He specialized in eerie folklore of New England. Many of those tales are being updated by Jeremy D’Entremont, who has a commitment to authentic stories.
– Nick Redfern isn’t a ghost researcher, per se. In fact, he wanders into UFOs, lizard creatures, and so on. In other words, he rarely talks about ghosts and ghost hunting.
Now and then, I browse his books because I believe we need to look outside the ghost hunting field. That’s the only way to maintain a healthy perspective on some of the truly weird things we encounter.
But many (most?) of his books, such as Paranormal Parasites, make me raise an eyebrow. (That’s an understatement.)
I mention him because some of my readers absolutely love Redfern’s deep research and his writing style. I think he’s one of the best in his field; it’s just not my field.
– And, in fiction, I still like The Haunting of Hill House, by Shirley Jackson. It may be my all-time favorite ghost story.