Adjusting My Chain of Network Advertisers

I haven’t evaluated the chain of my network ads in some time. We been selling some direct campaigns.

But we have a lull now and I want to get the best CPM and performance I can.

Currently I have TribalFusion, Burst, ValueClick.

TF I’m getting a great fill rate but not great cpm.

Burst has a terrible fill rate.

Is there anyone I’m missing that I need to substitute for? Are there other networks now that I should look at?

Thanks!