Much better than the Maltese Falcon, mostly because I just find Nick and Nora Charles to be far more engaging leads than Sam Spade, and the entire Wynant/Jorgenson family was quite the delicious mess. The actual mystery isn't really all that more compelling, but the cast seems a reasonable basis for choosing this novel over the other, as I'm coming to see that Hammett is also more interested in people than in material clues and crime scenes and detection. A lot of his clue-finding and action is off camera while his protagonists are mostly intuitive psychologists, working the rest of the cast off eachother until a picture emerges. And Nick and Nora just do this with much more wit and style than Spade, I think. 
 Still nothing that can even approach the gritty elegance of Chandlers's descriptive prose, though.