People often ask me about the best theme or design for AdSense.
That really depends on your goal. If you want to add AdSense to your header then you should find a design that makes it easy to add the code.
I use the Magazine Pro WordPress theme on my hair site. It has a header widget built in that is large enough to fit the 728x90 unit so adding the banner was a breeze.
Changing to this theme more than doubled the earnings for that site because I was able to add the large, header unit. Larger units typically earn you more, especially when they have good, visible placement.
