Long before I ever read The Hellbound Heart by Clive Barker, I had seen the movie version Hellraiser on cable. Hellraiser was only one of several stories in the book, but it's what made me want to read the book. It went the same way with The Stand, Carrie, etc. I had always ended up seeing the movie first.
I guess as a child, I was a much more visual person because when it came to horror, the movies always came first. I soon came to realize that many of the movies I loved to watch were actually based on books or stories in books. I voraciously began reading everything I could by King, Barker, Koontz and others.
It wasn't long before I realized that the books were vastly different than the movies. The books had more details, more plot points and were much more thought out than the movies. Movies were like a shell of the books. Screenwriters took license with the plot and characters in order for them to fit within the time allotted and into modern conventions of movie magic.
I still don't know which one is best. I love them both for different reasons. It's like the Team Jacob and Team Edward dilemma. If I had to choose, then I would say that books were my preferred medium. There's something about exploring every aspect of a character that is appealing and you just can't do that in a movie. At best, a movie can truly focus on only couple of characters and everything else is background.