I've read Ulysses twice now. I liked it better the second time. It may be the best book I've ever read, but it's a tough call. It's monstrous, yes, but it's masterful. I don't think anyone can top Joyce's command of the English prose nor should they - Finnegan's Wake is (disclosure - haven't read it) that kind of monstrous overreach.

If not the best book, it's definitely the greatest book, if such a distinction makes any sense.