I've read many Ruby books over 6 years. The best, in my opinion, is David Black's "The Well-Grounded Rubyist". I read it just last year as an experienced Rubyist. I thought it had a fantastic, no-magic take on the language that offered a better perspective on scope, metaprogramming, and general language design than any other book I've read. That said, I haven't read the Matz book.