Text Links Versus Image Ads
In general, text ads tend to pull a lot more clicks than image ads, because people have become “banner blind.” That means people have learned to ignore banners, because they know they’re ads.
Text ads are a part of every website, so they’re harder to ignore. This is one reason why AdSense is so successful. Of course, some sites could benefit from a few image ads. If your site is primarily text, you might be able to make it look more appealing through the use of a few graphical banners.