Just what the title says.
I want a book that gives me an impartial opinion of each president's time in office and presidency as a whole. I understand that it's sometimes difficult for impartiality when it comes to this, and that true neutrality on the subject is hard to come by, but anything you guys can offer is greatly appreciated!
One of my go-to's is The Complete Book of U.S. Presidents by William A DeGregorio. You're absolutely right that it is hard to find a non-biased book but this one does a pretty good job of explaining each in moderation.