I remember that I was very disappointed when I got my copy of Pirc Alert a few years back, lots of pointers for low rateds and some TNs thrown in, but the range between these two opposites wasn't covered much. It felt strange looking in a theory book and not get an idea of how the theory as a whole looks - especially considering the size & price of it!

Nunn/McNab or Nunn's earlier works on the Pirc are quite OK and very informative, though it's been a while since I looked at these.

A book I really liked is Norwood's Winning with the Modern, it's probably even more dated than Nunn/McNab, but still a good read I think, if it's still in print...

Gallagher's Starting Out: Pirc/Modern is a must-buy whether you are starting out in the Pirc or not. 

Alburt is good for explaining the key ideas of the Pirc. It's the only opening book that devotes so many pages to themes arising from the opening. However, I think Gallagher is just as good in this area using much less pages. From where I come from, Gallagher is also half the price of Alburt. So it's a no-brainer which one to choose.

Nunn/McNab is one of the most wordless (and hence boring) opening book I've ever seen. Only for the advanced player who already knows the main ideas and wants to check theory.

The problem is that both Nunn/McNab and Alburt are slightly dated. They don't cover new developments in the Classical/h3 Pirc, 4. Bg5 and Austrian. This is not too serious and both are still good. But I would hesitate paying full price for either, especially the Alburt which costs a bomb.