I think there has been something written after Nunn/McNab, a book that's very dry and theoretical in my humble opinion - Pirc Alert was well received in many quarters, and is well worth a look for club level players and below. I quite liked it and found it very useful, although a large percentage of it's expansive page count was wasted on poor layout, so it's not as densely packed as you might think. I no longer have my copy of this, but seem to remember it covered the 150 attack well.
And if I may quote Rowson's 'Chess for Zebras' he relates that he was chatting to Michael Adams about the 'various problems with 1.e4' when Adams remarked that there were indeed difficulties, particularly in certain Sicilians, saying 'well, you can't play against the Pirc every day'.
Rowson adds that the elite players consider it 'too generous to White', whilst noting that Pirc players should not take offence at that observation - they should simply accept that at the highest levels the defence isn't played much, and there's a reason that is so....but at sub 2500 level it probably doesn't matter, according to Rowson himself.
I think Stohl made a similar remark about the Pirc in his 'Instructive Modern Chess Masterpieces' book. So I suppose what I'm trying to say is that it is perhaps incorrect to think that it equalizes easier than any other opening (
) as condor suggests, and that the statistics shouldn't be trusted on that one..... The Sicilian would probably take the title of most likely to equalize, arguably.