Best pop up/under network

I'm an advertiser and I'm always looking for new opportunities to promote our clients.
Recently I started advertising through pop up or pop under on hundreds of sites, individual sites, and I continue to look for personal/private sites that sell traffic via this format.
However, pop networks allow me to get more traffic in a more quicker and info-centralized way.
From a publisher point of view, which are the best pop networks? I already do business with a few of the big ones as popads or…
Best pop up/under network

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