Forum Moderators: martinibuster
I can't see how there could be any negatives (costs or anything) for Google to provide additional formats.
The only way to know what will work best for you is to do testing. I advise testing different ad blocks in different positions for long enough periods that you have confidence in the stats. By using channels and assigning the channels randomly to a given page you can even run tests on the same pages at the same time.
However, in choosing that method, I still try to make sure that I don't exceed a total page width of 800 (for people with smaller screen configs). It's bad news to have ads that people have to scroll to the right to see. So in certain cases (such as my online commentary -- yes Google approved me running my ads there) I use the skyscraper, as squeezing in my commentary with pics and what not along with my leftside navigation bar proved cumbersome. But long story short, if possible I recommend the wide skyscraper on the right top underneath the header.