Hold on. The order that Google places ads inside your ad blocks is not dependant just on the highest paid ones going first. Google puts the BEST ones first, and their idea of best is the ones that make them the most money. Best is probably worked out something like "click-value multiplied by convertsion-rate". So a lower paying ad could appear before a higher paying one if it converts really well.
About different ad sizes, I have now standardised on the large rectangle, as it always does best for me.
I don't agree that a certain ad size will do best WHERE EVER it is placed on the page, because ones below the fold get pretty much no clicks. Also, Google's heat map and Jakob Nielsen's reading map indicate that people do look at the top and left column of pages more than they look in other places, which implies that they will see the ads more there and click them more. It's common sense really -- which story in a newspaper gets looked at more, the front page main news article, or something at the bottom of page 11?
