If you are interested in earning revenue for your website via ads and ensuring your advertiser is pleased with the click through numbers and impressions you may want to read this white paper Power of Clean by Say Media. They prepared a comprehensive and easy to read document backed by research to settle the issue over whether 1 or 3 ad's placed on your website will net the best response and impression. The short story is: 1 well designed clean ad (an ad that adds value to the user experience) on a crisply designed webpage will net the best results.
Based on eye-tracking data, 100% of users noticed the Clean ads, and they spend more time with these ads.
Read the Power of Clean white paper for all the juicy data.