When you read a fiction novel, the following things occur in your brain. First, your brain tries to visualize what is going on in the book. It immediately puts in information of what the characters might be-what the setting might be, and other than a tv show, it doesn't give you the facts straight off so it isn't being lazy. Second of all, it improves your reading skills, which by consequence makes you a more effective communicator. It also tends to have lessons you can learn, and expand creativity and innovation within yourself. And finally, it doesn't nearly as much ruin your eyesight.
Reading a novel forces you to imagine what is happening rather than just viewing it. I read in one of the New Times Articles that reading develops your empathy skills because you have to imagine what the character is feeling in a situation. Also, while reading, you notice the structure of writing so you become better adapted at writing yourself.
One example I have picked out was the shining by Stephen King. The fact that you get to imagine most of the book, you pick out the best situational setting for the book as opposed to actually seeing it in person. I think the book was much scarier compared to the move.
As a writer and reader, I can say myself that I feel more involved with the characters of a fiction novel than a television show. I know what they think, I can empathize with them and the way it is composed is pure magic, I can see scenes more vividly than a screen could ever dream to portray and feel feelings no acuter could draw from my heart. Books are simply better.
I find that reading textbooks for me is hard I am unable to absorb anything. I'm currently reading fiction to hopefully increase my reading comprehension skills and speed to hopefully understand the textbooks that I must read for school. I found that before I began reading fiction I found it impossible to pick up a book and immerse myself, rereading every line of text because my mind would always drift. Now I can pick up a book and remove all the distractions around me easier.
In both forms, you are being told a story. Add in other forms of media that do this, like storytelling verbally, video games, and music.
The point of the activity is to tell a story. Both have advantages and disadvantages over other forms of entertainment, and I would argue no form is intrinsically superior to the others, they can only be contextually better.
Since the question does not offer a situation, I can do nothing but disagree with the initial premise.
OK, generally it all comes down to the person and the situation, so there are arguments for both sides. Personally however, I'd almost always prefer the TV show.
Let's face it: No matter how much we believe we could imagine a situation better when reading a book, I doubt this can ever be true. If I asked you to draw the protagonist of the last book you read, could you - being totally sincere - do it to the same extent as having actually seen a person in a movie without making up additional stuff as you draw? Fact is, we as humans can only imagine, what we have already seen before in one form or another. And that's why our imagination can benefit much more from visual media.
Also, if you claim watching TV doesn't make you think at all, maybe you're doing it wrong. Sure, you have to keep track of everything that happens (so your brain is busy after all), but when you have watched the show, no one keeps you from thinking about it. I remember having seen an episode of 'Supernatural' featuring a love spell and thinking about the moral implications (if love spells existed) for a week.
So, for many of you reading a book may be more entertaining, but as I can only speak for myself, I'd watch the show (if I could choose a good one; there are many downright annoying shows out there, of course).