I’d also recommend avoiding Findwhat. I’ve heard they used to be one of the better ones, but the results I’ve seen from them have been dismal. As bad as with Kanoodle and ePilot.
But no one is worse than Xuppa.
Be very leery of what you see on sites like payperclicksearchengines.com too. Those aren’t really reviews of PPC engines (at least not based on quality of traffic sent); those are affiliate links.