Do you think the PPC management industry has matured to the point where industry leaders have emerged? If so, who would you identify as those leaders? As a secondary question, if you were in the market for a PPC management company would you prefer to work with a large PPC management company or a smaller "independent" type company?
The market is no way near mature and it is very early days in the industry. As to market leaders I think Efficient Frontier is in the lead at the moment but it is just the start of the race. It depends entirely on your budget. If it's more than $5k/month go with EF. - Michael
GFC, my opinion is that you need expertise and attention not scale. Hire a company appropriate to your own scale.