When I take my daily walk through my subscribed webmaster forums I happen to see lots of questions about placements of Adsense ad units. Many ask for reviews, some want to know the best performing units and others want general guidelines. Most of the time someone posts the Adsense heatmaps that have been posted on the official Google Adsense blog or tell the person asking the question to use the large or medium rectangle unit and blend it into their design.

From my own experience I can tell you that the large rectangle blended into the main content of my website works best on all of my blogs. This does not necessarily mean that it will perform best on your website as well and it is always recommended to try different ad units before you come to a conclusion.

I’m always using WordPress blogs and I use a plugin called Adsense Paster to test ad units. Adsense Paster uses text files that are randomly selected. What I do is I create a text file for every ad unit that I want to test and let Adsense Paster do the rest. All units get the same amount of impressions and it is easy to pick the best performing one using the statistics offered at the Adsense website.

I would like to add that other advertisers can also be added to the text files which means that you can test Adsense next to Adbrite and Chitikia if you like.

Traffic levels are really important to judge the results. It’s probably not a good idea to test ad units if you get ten visitors a day because the results can’t be generalized from that amount of visitors and I do not start testing ad units until I reach 100+ visitors a day, the more the better. I prefer 1000+ per day to be able to make a decision.

I do not remove all ad units at once but only the one that is performing the worst. If I have more ad units at hand I replace it with another unit. If I do not want to try another ad unit I remove the text file for the ad unit that is performing the worst and change the options in Adsense Paster accordingly.

This way I can see what happens if all ad units get more traffic and make a decision after I can take a look at those statistics. I personally use Adsense Paster for this purpose. Once I found the best performing ad unit I place the ad code directly in my WordPress code and disable the plugin. No need to run a plugin if it is not needed.