If your website gets a lot of traffic but have low click through rate (CTR), then using a CPM ad network may be more profitable. CPM ad networks normally pays a fixed rate per 1000 impressions your ads get. On the other hand, if you have a high click through rate, then you may get more revenue from CTR ad networks such as Google Adsense. CTR ad networks normally pays a variable rate for each click you get. The pay varies from ad to ad and depends how much the advertiser’s CTR price is.