The fact that they are reliable - I've used several other companies in my time but none had such an incredible success rate as these guys! They were able to get us ranked for multiple keywords at once which was crucial given our competition level (we're working with clients who charge millions). We didn't want any middlemen/marketers so we could deal directly wtih Google ourselves without wasting hours chasing down errors or dealing with endless promises made over e-mails etc from someone else's marketers / team members.