Books are generally more reliable, Internet is quicker
as they had to get some publishing permission, and generally take a while to construct. On the internet, mis-information can be spread like wildfire. Sites go up, go down, with a regularity that is astonishing. Its difficult to find reliable sources, especially when you go deeper into subjects.
But if you want a quick answer to "who was that guy in that film?" internet is FAAAR faster.