As a partner or vendor for Human Resources, how do you differentiate your business and define your unique value proposition?

I've been in business development for over a decade, with the last 5 years spent in recruitment advertising. Our company is the undisputed leader in our markets, though these are admittedly small markets (big fish in small pond here), and we enjoy a healthy market share.

As a partner for recruiting, the innovative tools we offer affect more than just the HR department- they affect productivity, employee retention, profitability, culture, etc.

My question is this- when you approach new prospective clients, do you enter through the HR office? Or through a different door?