This is a well done book that fulfills most of what you would buy it for: Exhaustive inventories of Jazz albums with relative ratings and many reviews.
However, a few things would make me suggest the Penguin Guide over it (I own both):
1-ARTIST INDEX / Personell listing: the single greatest reason to get Penguin instead of the AMG is that every listing contains a complete personell listing at the top of the entry. Then the index in the back refers to the personell on albums. The AMG may list personell in the review, and indexes artists by any mention of them whether they are on an album or not. Penguin's version is much better for Jazz, where an artist's best work may be on someone else's album. Using the Penguin, you can look up every album Jack DeJohnette has played on as a sideman, just by flipping to the page numbers listed. In the AMG you have to wade through reviews (and many albums don't have reviews) which may just compare Jack's style with whoever is drumming on the record being reviewed.
2- Not every album is reviewed. Many albums are left only with ratings and no commentary whatsoever, which can be frustrating if you are wondering whether to buy a specific album. WHY did something get the rating it did is more important than the rating itself.
3- Consistency: The Penguin guide is written and judged by 2 men. As you go through it, you learn their biases and can glean more information about whether you'd like an album even if they give it a low score.
4- Mistakes. There are several mistakes in the AMG. For example, calling Speak Like A Child Herbie Hancock's last album for Bluenote a paragraph after reviewing the Prisoner.
To be fair though, there are advantages to the AMG:
1- The Penguin Guide limits itself to CDs out at the time it is published. This means you are SOL if you buy vinyl or used cds that have since gone out of print or if an album is rereleased after the Penguin Guide date. I think the AMG lists all albums whether they are currently in print as CD or not.
2- Tutorials. The AMG has essays in the back describing the many genres and time periods of jazz. In the body of the text are nice charts of the evolution of individual of instruments, from Saxophone to Bagpipes. Interesting though not vital if you are already into the music enough to need a definitive listing of albums.