Not including short story collections, poetry collections, anthologies, etc.
For me, I believe it’s Oroonoko by Aphra Behn because it was on the syllabus for three different classes that I took in college. Other than that, the most I’ve read a single book is twice, and that was Telegraph Avenue by Michael Chabon. I’ve read Dracula 1.5 times. Didn’t finish it the second time around.
All my most read are books that I read in my teens and have revisited every few years cos of the comfort factor. Childhood really does shape you for life. Gone with the wind, Wuthering heights, some Jane Austen for when I need something breezy, a bunch of Agatha Christies when I need to feel like I’m home and without problems in life.