When you bring up the best adsense layout for a high CTR many people will start to tell you to use the 336x280 on top of the fold and a 160x600 skyscraper on the right side. This seems to be the standard advice that is given out. While it is good advice there are other ad formats that can be implemented to improve CTR'S. Those ad formats are the link units.
When i look around at other niche sites trying to make money with adsense i do not see the ad units used to there maximum effectiveness about 80% of the time. In my opinion people tend to throw them up as an after thought, hoping they bring in some money once in awhile! Well if placed right the link units in adsense can dramatically increase your earnings.
My strategy for link units is very easy and used by some of the top earners in adsense, in fact i was doing it before i knew who the top earners were!!! My bubble was sure burst when i found out i hadn't came u with something new and unheard of!
What i do is a use the 200x90 link units and set them to display 4 ads. If you set them for 5 the font is so small you can never get it to look natural on your site. Place the ad link so it blends either on top of or on the bottom of your website navigation links. When done correctly they blend right in and people assume they are navigation links.
Another good strategy is to put the 728 x90 link unit across the to of your age under the header. These apar to be more navigation links and peole will click them as well, and quite frequently i may add.
However keep in mind that with the ad units you only get paid if they click on the google search results after they click the links on your page. The links on your age are basically a portal to another ad page. To date my CTRS have been very good with this method and my earnings have increased as well.