I've had good success with Rain King. They seemed to have the most updated and a lot of good information that you got beyond just the lead name. Of the tools you mention, Data.com seemed to have the most quality leads. The occasions when I used Hoovers, all of the data was extremely old and incorrect. InsideView is also nice for some deeper info beyond just the name. And it's integration with SFDC, if that's your CRM, didnt hurt.