Ulysses is unreadable, but more readable than Finnegan’s Wake.
Atlas Shrugged? Readable again and again. But I would not have voted it the best.
I vote for Asimov’s Foundation Trilogy.
That’s like saying rocks are indigestible but more digestible than razor blades.
Dubliners is readable. A Portrait of the Artist is readable. Ulysses is supposedly great literature, but I could never suffer all the way through it. Finnegan’s Wake? I’d rather spend an hour listening to a rabid paranoid schizophrenic yammering klang and word salad phrases. It would be more pleasant and intelligible.
As for Atlas Shrugged, it’s easily readable. It has that potboiler quality (and I mean that in a good way).
How about Tolkien's LOTR trilogy?