I want to go on record saying that anything by O'Reilly is generally good to great; they're an amazing publishing company with a very competent editorial staff. Wrox has really fallen off in the last few years. They were once good, but recently they've focused on publishing books that champion any new buzzworthy technology, books that they rush to the shelves in hopes to win sales through novelty what they've sacrificed in quality control. O'Reilly is more likely to be late to market, but with much more substantial material that isn't riddled with typos and code samples stillborn with compilation errors. Of course, there are also many great small press publishers as well.