I can't remember which one I read. I have a vague feeling I managed to get an old copy from somewhere. So it may even have been the 1st Edition.
I'm not sure what the differences are between the editions, but if the author has seen fit to go back and change a few things, and unless anyone specifically warns me against it, I'd choose the newest one.
Seeing as the authors collaborated on the PSU course, if anything, I expect the newer edition would describe the relevant concepts better. Also, regardless of the exam, it's probably better for your personal development, to receive the most up-to-date advice, as the expert authors have had time to inspect & adapt their work and the impact it has had.