From months i was testing best ad placement and best ad site for adsense on some sites and result is Ad placement : Text ads between content. if you are a blogger then just place after every post. Ad size : I got to know 336*250 gives most. If someone else have any tested idea share here. I will share more secrets. So keep looking my threads.
While in an overall sense adsense works best when it is naturally blended into the design of a web page, the ads must have a bit of air (or "space" as noted here earlier) around them. If in your navigation of pages includes the idea that your visitor is going to quickly thumb through a lot of pages one after the other, then change up the ads on that page if ads are all in the same page location. The idea is that Adsense might serve up the same 200x200 image ad over and over on a sequence of pages and that is not necesarily good. Change some to text ads to give the visitor a more varied adv choice and experience.
your tests are correct.. i tried too.. and skyscrapher text only ads in the rightside / leftside will work best with good CTR ! blend it if possible.