Burning Question - Mastery or Bestiary?

In my last {Quest Log}, I mentioned that I was going to buy the Pathfinder Bestiary and I was about to take the plunge and place an order when something else came up and is vying for the cash that would be spent on the Bestiary.


I've read a couple of good things about the Pathfinder Gamemastery Guide and these are coming from people (Greyhawk Grognard, NewbieDM) who don't even play Pathfinder, which goes to show how useful the book is.

However, what I'm more interested in, as someone who is planning to run Pathfinder, is definitely the crunch elements in it. This review from Stargazer's World certainly shows that it isn't really lacking in that department as well.

From what I gathered, it's a book that is choked with great advice from a plethora of the best GMing books out there together with useful mechanical tools for running the game. So, it's a good book to have for some casual reading (and what more appropriate time to be doing that when I'm in the middle of a gaming drought) and I'm sure I would get a great deal of use out of it when I'm running a session.

On the other hand, the Bestiary has monsters...more than 350 of 'em.

Although I haven't seen any reviews about this one but you don't really need any convincing, as a GM, to buy a monster book. Crunch-wise, a book like the Bestiary is as crunchy as a box of breakfast cereals made out of dead PCs for evil GMs. It's a book that you damn sure know what's going to be in there and you know how much you need it.

Then again, there is the promise of finding gorgeous artwork in a book that comes from Paizo.

Although at this point, I'm going to put the Bestiary into the backlog since I can still peruse the Bestiary SRD in the meantime but I'm interested in hearing your thoughts on which book would you prefer?

If you had to pick one, would you prefer a book of GMing advice and tools or a monster book to pounce on your players?