The simple answer to this question is that Google ads manager who bring new customers for you.
Google ads is a technical ads platform so as a business owner you should focus on your return of investment rather than understanding the technicality of how the ads platform work.
If you invest X amount in Google ads to generate business, are you getting X+Y?
But, many PPC agencies try to hide the ROI from their campaigns under the vanity metrics like impressions, Clicks, CTR etc.
As a general rule of thumb, you can ask for a test drive from the PPC ads Manager before deciding one for long term relationship.
This way you will be able to see which PPC service provider works best for you.
But let me warn you about 1 common mistake businesses commit in selection of PPC partner, they go for the cheaper service provider who claims to offer superior service at low cost but fail to deliver on his promise.
Good PPC ads Managers are in high demand and don’t come cheap but the fees you pay for their service is well worth it because a Good Google ads Manager can save you thousands of dollars on unwanted clicks and improve your ROI which should ideally be your end goal as a businessowner.