I can say with absolute certainty that Harry Potter and the Half Blood Prince is the book I have read the most.
It’s my favourite Harry Potter book for so many reasons. I love Slughorn, the fact Snape finally gets his dream job and finding out about the horcruxes. During the run up to the movie adaption I must’ve just sat and read that book over and over again. I still have my original copy on my book shelf but I’ve read it so many times the cover on the spine has actually fallen off. I should probably buy a new copy. I don’t think it will survive if I try reading it again.