These two are the only ad services other than Facebook Ads that I'm familiar with. I'd be open to suggestions on other services to try, and would welcome them. AdSense and Project Wonderful run differently enough that I'd be interested to see whether other services emulated one or the other or innovated something else entirely.
Ads on a website or blog are excellent tools for any independent author, editor, or assorted indie-publishing related person to earn at least minimal returns whether or not they are making sales.
In an ideal world, of course, we'd all be millionaires from our book sales. In the meantime, smoothing out the times between royalty checks and payment threshholds from author services websites is something we can all appreciate.
I installed AdSense first because it's so conveniently integrated into the Blogger platform. From my end, the tabs to post and monitor settings are right next to the tab governing the AdSense interface with Blogger. They won't pay me until I've earned a hundred bucks, though, which is something Project Wonderful has on them: Project Wonderful will pay up if you've earned at least ten. Another thing I like about Project Wonderful is that I know people who advertise through it: writers I know, comics I read, games I play.
Which is another reason I installed AdSense first: unless Project Wonderful earns me exponentially less than AdSense, I will probably stick with it when I install it.
I can't run them concurrently because of AdSense's terms and conditions, sadly.