Image Ads vs. Text Ads
Back in 2004, Google announced an expansion to its Adsense program and it entailed incorporating image ads into their ad units. However, it has been difficult for most new adsensers to determine the performance of image ads versus the proven performance of text ads.
Graphical ads work well but not with all sites. Adsense publishers have image ads available to them but they do not have the option to choose whether their site will show still image ads or animated ads. How do you then figure out if image ads perform better than text ads? This is my formula, take a look at the huge sites that use adsense on their pages. Myspace, hi5,and friendster to name a few of the big social networking sites all use the text ads extensively. I believe this is proof enough that text ads yield better results than image ads though one may argue that on a photography site for example, image ads will yield better results. The point here is text ads have been proven to perform better than image and even video ad types. My advice, if you want to try out other ad types, use them in conjunction with text ads, establish channels for your ads and monitor the performance of image ads against text ads. I would advise a 30 day trial period. This should be sufficient to determine what works for you.
When it comes to the argument of which ad types and units are successful, I personally think it all depends on the type of site you own. This is because on some sites the leaderboard for example would work better than the large rectangle whereas on another site, the large rectangle would work better than any skyscraper ads. This is why it is important to understand your site and what you want to achieve from putting adsense on it for your visitors. Adsense publishers must take into account the long term goals of their websites. One of those long term goals should be to publish content that ensures repeat visitors and thereby maximizing profits.
Hope this post was of help to you.