There’s a useful post over at the official AdSense blog titled CPM ads: Knowing the facts can pay off which busts some of the myths circulating out there about CPM ads (ie ads that you get paid for per impression rather than per click).
The main points in the post:
- both text and image ads can be both CPC (cost per click) or CPM ads.
- AdSense will run the ad that has the highest probability of earning the publisher the best price if it’s a choice between a CPC and a CPM ad on your blog
- if you select ‘image only’ you do not guarantee to only get CPM ads
- AdSense recommend you allow both image and text ads to get the best revenue potential (there might be reasons to go one way or the other though in my opinion – see below)
- You only get CPM ads served to your site if an Advertiser has specifically targeted your site
The main reason I say that it can be worthwhile either choosing image or text ads is more to do with the aesthetics of the ads and how they fit into the design of your site. While you might earn more by allowing both image and text ads if it doesn’t fit with your design you might not want to go this way. For example – on some blogs image ads tend to dominate the design too much as you have no control over how they look. If your blog’s design is subtle and clean text ads might well be your best bet.