CPM Ads Vs. CPC Ads Vs. CPA Ads

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You can monetize your website through different kinds of ads. CPM ads means you earn x amount for every 1000 ad impressions, CPC means you earn for every legitimate clicks on your ads, and CPA ads means you earn when your visitors take action on your ad, which could be signups, purchase, etc. Between these three different kinds of ads, what do you think will let you earn more? Have you used all of these advertising methods.