I don't think I can give you a simple answer to your question. I don't see a clear way to do an apples-to-apples comparison of a film and a graphic novel.
The movie was extremely true to the source material without coming off as a slavish reproduction. I'd say that, in some ways, it is the best "comic book movie" I've seen.
I think I'm safe in categorically stating that the book holds a higher place in the pantheon of graphic novels than the movie does in the pantheon of films. In that sense the book is better. I suppose that, if you like graphic novels and films equally, the book is better. I think some of Frank Miller's art is shit (looking at you, 300), but some of my all time favorite panels appear in The Hard Goodbye.
Having said that, if you've seen the movie there aren't going to be any big revelations in the book. Unlike, for example, the film adaptation of The Return of the King, which leaves out The Scouring of the Shire. To me, that's the most important and meaningful part of the books.
Based on my assumptions about you and the context of your question, I suppose the answer is no. On the other hand, as a guy who finds something special in the work of one guy with some scratch board and a something really different to say, I think I like the book better.