Conventional wisdom says that for an Adsense publisher to make money, he or she should be using the 336 X 280 ad format at the very begining of their articles.

Everytime I used that format, not only did my earnings significantly decrease, but all my the other ad blocks earnings decreased.

What were my best performers?

Adlinks! The sheer volume of clicks produced made up for the lower price.

Tower on left. I thought ad blindness would have killed the format. But although I didn't get nearly as many clicks, the CPC was significantly higher.

The moral of the story? Take the time to optimize your site for the highest revenue return you can get. If you are not getting a higher click through rate, your ad format probably isn't working for your site.