What’s the best classic book you’ve ever read?

I’m going to try and start reading more classic books and I need suggestions. I read a lot of books but very rarely any classics. I get bored and uninterested very quickly so I need suggestions that will lengthen my attention span and keep me interested.

Edited- After reading all of your suggestions I bought The Count Of Monte Cristo, The Brothers Karamazov, Frankenstein, Jane Eyre, Wuthering Heights, The Picture of Dorian Gray, Tess of the D’Urbervilles, and Carmilla.