Which one of the following do you think is the best adsense placement strategy?

Placing ads at the top of the page
Placing them in the middle
Placing at the end
Placing in the navigation menu
Placing in right skyscraper

I think that placing in the navigation menu is the best strategy.

I think that placing them in the left skyscraper is best because they appear to be links and not ads if placed at left side of the webpage. Generally any webpage contains links to on the left side. Placing ads on the left is a simple and effective idea. The top placement is also useful provided proper coloring is used. Because it also creates the impression of being some links to the visitor increases the chances of clicking.