I like both, reading the book and seeing the film, but sometimes the film is very disappointing. I'm a big Lee Child/Jack Reacher fan and have read all the books and stories so far. I found the first film disappointing, since Tom Cruise is nothing like my mental picture of Reacher, but adequate. But the second film was awful. They changed the story and made it really trivial. I didn't watch to the end. Films rarely have the subtleties of books, but they can be good in their own right.

I watch almost exclusively fiction when watching films but real life when reading books, mostly crime, serial killers, and generally evil people. some actors just spoil it for me like Will Farrell for instance.

Saw the first of the Twilight series then read the book. Then saw the other 5 movies.
Saw 50 Shades of Grey and 50 Shades Darker because I liked the cast.
Read Godfather before the movies-loved first two films.Third was disappointing.

The movie that plays in my head when I read a book is so much better than what other people can create.

I would rather read the books.