Best Adsense Ad Format / Layout

The best ad format is that which integrates most visibly and most seamlessly into your targeted webpages - and as this context is very variable, so will the preferred best options for those targeted pages.

Best Performing ads formatted to look like it is part of your site, not an ad. Ads should be used based on page content. Primarily, use of a combo of leaderboard, skyscraper, and rectangle is best. Ad size depends on the content of the page. I may use rectangle for an article, leaderboard or skyscraper for ordered/unordered lists.

The wider format lets them comfortably read more text at a glance without having to skip a line and return to the left margin every few words as they would be forced to do with a narrower ad. The wider ad format also lessens the likelihood of readers leaving the ad unit altogether.

There has been lots of speculation about the best performing AdSense ad unit sizes, and the 336x280 has always been the best ad unit size. But even the best performing ad unit size will not perform well on a site if it does not suit the page layout.