Depends on the site topic and where your visitors come from. For me, both Adsense and YPN make about the same.
I Like Poem says, it depends on your niche...I don't deal with adsense anymore, YPN has been making me more money...
At first Adsense ruled for me, then suddenly along came smart pricing then 3 cent clicks etc. Next I got into YPN right after it launched and was enjoying $1 clicks for a long time and high earnings. Now YPN has been slowly decreasing over the past 7 months or so for me, and I am almost making the same with ypn as I can or do with AdSense, and that's not very much. There were some past days (months and months ago) when Id get $60+ a day, anymore I am very glad to make over $10 a day and that's with multiple websites combined.
Why not just do both? Send US traffic to YPN, international traffic to Adsense? It works, and I actually make more eCPM with Adsense after doing it (which is weird... but whatever)