As the author of StolenCameraFinder, I am somewhat biased ;)
Both sites have published success stories. Here are my success stories, and here is one from CameraTrace. I actually have more stories in my email, I'm just pretty rubbish at typing them up ;)
With both sites, you can run searches for free manually, just try them out and see what results you get. You should at least get results showing photos you've taken. The more photos you have online, the more likely our web crawlers will have found some. We don't have the resources of Google so we haven't crawled the entire internet (yet!). Instead we optimise our searching to be wide and shallow rather than deep and narrow. That's a good thing because you only need to find one photo that was uploaded by whoever now has your camera to be useful in recovering it.
You can help the search for stolen cameras by installing the Chrome extension along with >20k other people.
I suggest you just use the site for free and only pay for the Pro features if you see photo results that you didn't take, or you want the email notification feature. (I'm a rubbish businessman!).
Good luck and please let me know how you get on. -Matt