Their ability to help us find quality talent quickly, and in many cases before we even got started! They are also very good about providing feedback, so they're not just another tool that we can use when looking for candidates.
I wish there were more options than "web" or "email." While this is the most efficient way of finding leads at first glance it doesn't give you as much control over your search criteria. So be sure to get into their system, but don't lose out on other ways to access potential candidates either! There's no one thing specific - when working with them though, everything worked great. And being able to filter our searches by skillset really helps save time!