What is the Best Header Bidding Solution?

We get emails daily from ad networks or people who say they are an ad network offering solutions to raise CPMs.  As a small publisher, it is very difficult to understand what ad networks actually offer a competitive service to Google Ad Sense.

What is the best header bidding solution for small publishers? Is it better to go with multiple ad networks or just one like Appnexus or Pubmatic?

Over the last 10 years, I have watched our traffic increase steadily by 15%+ per year.  However, our advertising revenue from Google and Media.net has stayed fairly flat and has not increased much at all.   Is this because Google is continually taking a bigger piece of the revenue share?

We have heard that header bidding is a solution that can increase CPMs by 2x or 3x depending on the traffic.  Is this true for someone in a niche map crowdsourcing publishing space?

Please email me if you have a solution or suggestions.