What is a best tone of a viewer of a book review

Ok, first let's understand what tone actually means. In the dictionary it says that "Tone i s the way the author expresses his attitude through his writing." - YourDictonary

So, the tone of a viewer of a book review would be ... how they express the attitude through a book review! Then answer put the question this way.

"Which is the best tone?"

Tone means the authors attitude, or the feeling the author wants the overall mood of the passage or book to be. So, probably a positive tone.