I highly recommend PropellerAds whether you are a website owner or an affiliate marketer. I'll be explaining my review both as an Publisher and as an Advertiser.
Publisher: PropellerAds has great tools to help you monetize your website. My favorite happens to be push notifications. It helps me have an asset of subscribers and I can make money by promoting these subscribers push notifications from advertisers or by CPS. Also setting PropellerAds on my gaming website is pretty easy to install.
Advertiser: PropellerAds has a lot of advertising methods. You can do Popunders, Native Ads, Interstitial, and PropellerAds. PropellerAds also features SmartCPM and SmartCPA that suggest on which website is giving out the most conversions. PropellerAds also gives you estimate traffic and how much you should pay to get to the next threshold. Last but not least PropellerAds is pretty cheap to set up campaigns. For $10, I can get 20,000 impressions with $0.5 Popunder CPM. The only downside to PropellerAds is bot traffic, and bot traffic is definitely annoying. The best solution is excluding source IDs that produce high traffic but no conversions.