The choice depends on age groups and kids interests. Like my son he is 5, he is very much interested in playing. My daughter enjoys teaching. We can encourage them to read story books. By reading books they will explore new things.
Toys are equaly essential as fun and frolic are an inseparable part of childhood.
Books increase the horizon of knowledge. I would prefer to buy books, because it is the only source a child can have when he is growing. Books provide a large amount of knowledge. I would like to inculcate the habit, or I might say, a hobby of reading in my child. If a child is small i.e. below 7yrs then a toy would be a good idea,whereas if a child is above 7yrs a book would be nice.