I've been with AS and YPN since each of them started. I've done fairly consistent testing with both to see which pays better.
I have compared earnings on a number of different accounts (client accounts and my own) for about a dozen sites on a dozen very different subjects.
About 1/3 of the sites that I tested with YPN got very relevant ads all the time.
In the end, after random testing for about a year...
When I compare ad unit CPM and my bottom line, GA pays an average of 30 percent more than YPN on 10 out of 12 sites that I've tested both programs on. The 2 sites that made more with YPN made about 50 percent more.
I also see a lot more stability in earnings with GA than YPN for most sites.