With Samuel Delany, I think his best book is
Stars in My Pocket Like Grains of Sand, but it was written in the expectation of finishing the story in a sequel that isn’t going to happen. So I’d suggest starting with the brilliant and self contained
Babel-17. Actually, I think I’m going to say the same thing I do with Heinlein feel free to start with anything where the book is less than an inch thick.
Charles Dickens don’t start. No, that’s unfair.
David Copperfield are his least unbearable books, and where you should start if you feel you have to. The reason they’re less unbearable is because they’re first person and not the horrible version of omniscient he uses for most of his books.