These are the top 15 books in each of the main Doctor Who series of novels, as ranked by the number of people who own them on LibraryThing (also the top 15 non-fiction Who books at the end). Apologies to co-authors who fall off the list due to LibraryThing's practice of prioritising first-named collaborators compounded by my laziness in not looking them up.
Which of these Target novelizations have you read?
Which of these New Series Adventures have you read?
Which of these Virgin Missing Adventures, featuring the Seventh Doctor, have you read?
Which of these Virgin Missing Adventures have you read?
Which of these Past Doctor Adventures have you read?
Which of these Eighth Doctor Adventures have you read?
Which of these non-fiction Doctor Who books have you read?
Edited to Add: Bah, listed one book twice. The Face of the Enemy is of course a Past Doctor Adventure not a Missing Adventure. But you can't edit polls, so there we are.