Have you started to use Google AdSense new interface? If you don’t, it’s time to do so. There is lot of goodies there to explore. Just discovered ad types’ performance report there. And turned out that Google is telling the truth all the while ~ publishing text & image / rich media ads are better then text ads only.
Note – Page revenue per thousand impressions (RPM) is calculated by dividing your estimated earnings by the number of page views you received, then multiplying by 1000.
Based on the data above, clearly that text is the lowest performance ad type. As expected, the highest is rich media ad type, follow by animated image ad type then image ad type. Surprisingly, flash ad type does not perform well here.
As a conclusion, do publish both text and image / rich media ad types.