I don't normally both read the book and watch the movie. I tend to do one or the other. No particular reason, that's just what I do.
A few that I have done both:
- Jurassic Park: Movie was great, book was greater
- The Lost World: I remember watching the movie and thinking it wasn't as good as the book, but I cannot remember much about the book. Hmmm...
- The Princess Bride: Both book and movie were great, but the movie more so
- The Clan of the Cave Bear: The book was long and tedious but decent, the movie was garbage
- A Walk in the Woods: The book was great, the movie merely satisfactory
- The Hunger Games: The book was very good, the movie a significant step down
- Catching Fire: The book OK, the movie terrible
- Mockingjay: Both the book and the movie stunk
- Congo: Book and movie were OK
- Sphere: The book beat the movie handily
- The Hitchhikers Guide to the Galaxy: The book was good, the movie terrible
- The Martian: The movie was very good, the book excellent
- Pet Semetary: The book really sucked you in, the movie just sucked
I'm sure I must have done a few more pairs of book/movie, but my mind has gone blank at this point. In general, books beat movies most of the time. And you get a lot more bang for your buck in a book. They're cheaper than movies (usually), they last a lot longer (for me at least), and you can read them anywhere.
p.s. - One book that I really loved but would be afraid to see as a movie (I think they'd ruin the vivid imagery the book painted in my brain) is "Wool" (the omnibus), by Hugh Howey. If that one ever comes out as a film I would really want to see it, but would probably restrain myself from doing so, just because I don't think they could come up with anything to match what my brain conjured up!